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Showing 1-20 of about 23 results.
Dust, Gas, and Metal Content in Star-forming Galaxies at z ∼ 3.3 Revealed with ALMA and Near-IR SpectroscopySuzuki, Tomoko L.Onodera, MasatoKodama, TadayukiDaddi, EmanueleHayashi, MasaoKoyama, YuseiShimakawa, RhythmSmail, IanSobral, DavidTacchella, SandroTanaka, IchiDOI: info:10.3847/1538-4357/abd4e7v. 90815
Suzuki, Tomoko L., Onodera, Masato, Kodama, Tadayuki, Daddi, Emanuele, Hayashi, Masao, Koyama, Yusei, Shimakawa, Rhythm, Smail, Ian, Sobral, David, Tacchella, Sandro, and Tanaka, Ichi. 2021. "Dust, Gas, and Metal Content in Star-forming Galaxies at z ∼ 3.3 Revealed with ALMA and Near-IR Spectroscopy." The Astrophysical Journal 908:15.
ID: 159635
Type: article
Authors: Suzuki, Tomoko L.; Onodera, Masato; Kodama, Tadayuki; Daddi, Emanuele; Hayashi, Masao; Koyama, Yusei; Shimakawa, Rhythm; Smail, Ian; Sobral, David; Tacchella, Sandro; Tanaka, Ichi
Abstract: We conducted submillimeter observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of star-forming galaxies at z ∼ 3.3, whose gas-phase metallicities have been measured previously. We investigated the dust and gas contents of the galaxies at z ∼ 3.3 and studied the interaction of galaxies with their circumgalactic or intergalactic medium at this epoch by probing their gas mass fractions and gas-phase metallicities. Single-band dust continuum emission tracing dust mass and the relation between the gas-phase metallicity and gas-to-dust mass ratio were used to estimate the gas masses. The estimated gas mass fractions and depletion timescales are fgas= 0.20-0.75 and tdep= 0.09-1.55 Gyr. Although the galaxies appear to be tightly distributed around the star-forming main sequence at z ∼ 3.3, both quantities show a wider spread at a fixed stellar mass than expected from the scaling relation, suggesting a large diversity of fundamental gas properties in star-forming galaxies that apparently lie on the main sequence. When we compared gas mass fraction and gas-phase metallicity in star-forming galaxies at z ∼ 3.3 and at lower redshifts, star-forming galaxies at z ∼ 3.3 appear to be more metal poor than local galaxies with similar gas mass fractions. Using the gas regulator model to interpret this offset, we find that this can be explained by a higher mass-loading factor, suggesting that the mass-loading factor in outflows increases at earlier cosmic times.
Quenching as a Contest between Galaxy Halos and Their Central Black HolesChen, ZhuFaber, S. M.Koo, David C.Somerville, Rachel S.Primack, Joel R.Dekel, AvishaiRodríguez-Puebla, AldoGuo, YichengBarro, GuillermoKocevski, Dale D.van der Wel, A.Woo, JoannaBell, Eric F.Fang, Jerome J.Ferguson, Henry C.Giavalisco, MauroHuertas-Company, MarcJiang, FangzhouKassin, SusanLin, LinLiu, F. S.Luo, YifeiLuo, ZhijianPacifici, CamillaPandya, VirajSalim, SamirShu, ChenggangTacchella, SandroTerrazas, Bryan A.Yesuf, Hassen M.DOI: info:10.3847/1538-4357/ab9633v. 897102
Chen, Zhu, Faber, S. M., Koo, David C., Somerville, Rachel S., Primack, Joel R., Dekel, Avishai, Rodríguez-Puebla, Aldo, Guo, Yicheng, Barro, Guillermo, Kocevski, Dale D., van der Wel, A., Woo, Joanna, Bell, Eric F., Fang, Jerome J., Ferguson, Henry C., Giavalisco, Mauro, Huertas-Company, Marc, Jiang, Fangzhou, Kassin, Susan, Lin, Lin, Liu, F. S., Luo, Yifei, Luo, Zhijian, Pacifici, Camilla, Pandya, Viraj et al. 2020. "Quenching as a Contest between Galaxy Halos and Their Central Black Holes." The Astrophysical Journal 897:102.
ID: 157834
Type: article
Authors: Chen, Zhu; Faber, S. M.; Koo, David C.; Somerville, Rachel S.; Primack, Joel R.; Dekel, Avishai; Rodríguez-Puebla, Aldo; Guo, Yicheng; Barro, Guillermo; Kocevski, Dale D.; van der Wel, A.; Woo, Joanna; Bell, Eric F.; Fang, Jerome J.; Ferguson, Henry C.; Giavalisco, Mauro; Huertas-Company, Marc; Jiang, Fangzhou; Kassin, Susan; Lin, Lin; Liu, F. S.; Luo, Yifei; Luo, Zhijian; Pacifici, Camilla; Pandya, Viraj; Salim, Samir; Shu, Chenggang; Tacchella, Sandro; Terrazas, Bryan A.; Yesuf, Hassen M.
Abstract: Existing models of galaxy formation have not yet explained striking correlations between structure and star formation activity in galaxies, notably the sloped and moving boundaries that divide star-forming from quenched galaxies in key structural diagrams. This paper uses these and other relations to "reverse engineer" the quenching process for central galaxies. The basic idea is that star-forming galaxies with larger radii (at a given stellar mass) have lower black hole (BH) masses due to lower central densities. Galaxies cross into the green valley when the cumulative effective energy radiated by their BH equals ∼4× their halo gas-binding energy. Because larger-radii galaxies have smaller BHs, one finds that they must evolve to higher stellar masses in order to meet this halo energy criterion, which explains the sloping boundaries. A possible cause of radii differences among star-forming galaxies is halo concentration. The evolutionary tracks of star-forming galaxies are nearly parallel to the green-valley boundaries, and it is mainly the sideways motions of these boundaries with cosmic time that cause galaxies to quench. BH scaling laws for star-forming, quenched, and green-valley galaxies are different, and most BH mass growth takes place in the green valley. Implications include the radii of star-forming galaxies are an important second parameter in shaping their BHs; BHs are connected to their halos but in different ways for star-forming, quenched, and green-valley galaxies; and the same BH-halo quenching mechanism has been in place since z ∼ 3. We conclude with a discussion of BH-galaxy coevolution and the origin and interpretation of BH scaling laws.
The MUSE Atlas of Discs (MAD): Ionized gas kinematic maps and an application to diffuse ionized gasden Brok, MarkCarollo, C. MarcellaErroz-Ferrer, SantiagoFagioli, MartinaBrinchmann, JarleEmsellem, EricKrajnović, DavorMarino, Raffaella A.Onodera, MasatoTacchella, SandroWeilbacher, Peter M.Woo, JoannaDOI: info:10.1093/mnras/stz3184v. 4914089–4107
den Brok, Mark, Carollo, C. Marcella, Erroz-Ferrer, Santiago, Fagioli, Martina, Brinchmann, Jarle, Emsellem, Eric, Krajnović, Davor, Marino, Raffaella A., Onodera, Masato, Tacchella, Sandro, Weilbacher, Peter M., and Woo, Joanna. 2020. "The MUSE Atlas of Discs (MAD): Ionized gas kinematic maps and an application to diffuse ionized gas." Monthly Notices of the Royal Astronomical Society 491:4089– 4107.
ID: 155700
Type: article
Authors: den Brok, Mark; Carollo, C. Marcella; Erroz-Ferrer, Santiago; Fagioli, Martina; Brinchmann, Jarle; Emsellem, Eric; Krajnović, Davor; Marino, Raffaella A.; Onodera, Masato; Tacchella, Sandro; Weilbacher, Peter M.; Woo, Joanna
Abstract: We have obtained data for 41 star forming galaxies in the MUSE Atlas of Discs (MAD) survey with VLT/MUSE. These data allow us, at high resolution of a few 100 pc, to extract ionized gas kinematics (V, σ) of the centres of nearby star forming galaxies spanning 3 dex in stellar mass. This paper outlines the methodology for measuring the ionized gas kinematics, which we will use in subsequent papers of this survey. We also show how the maps can be used to study the kinematics of diffuse ionized gas for galaxies of various inclinations and masses. Using two different methods to identify the diffuse ionized gas, we measure rotation velocities of this gas for a subsample of six galaxies. We find that the diffuse ionized gas rotates on average slower than the star forming gas with lags of 0-10 km s-1 while also having higher velocity dispersion. The magnitude of these lags is on average 5 km s-1 lower than observed velocity lags between ionized and molecular gas. Using Jeans models to interpret the lags in rotation velocity and the increase in velocity dispersion we show that most of the diffuse ionized gas kinematics are consistent with its emission originating from a somewhat thicker layer than the star forming gas, with a scale height that is lower than that of the stellar disc.
Simulating JWST/NIRCam Color Selection of High-redshift GalaxiesHainline, Kevin N.Hviding, Raphael E.Rieke, MarciaShivaei, IreneEndsley, RyanCurtis-Lake, EmmaSmit, RenskeWilliams, Christina C.Alberts, StaceyK Boyett, Kristan N.Bunker, Andrew J.Egami, EiichiMaseda, Michael V.Tacchella, SandroWillmer, Christopher N. A.DOI: info:10.3847/1538-4357/ab7dc3v. 892125
Hainline, Kevin N., Hviding, Raphael E., Rieke, Marcia, Shivaei, Irene, Endsley, Ryan, Curtis-Lake, Emma, Smit, Renske, Williams, Christina C., Alberts, Stacey, K Boyett, Kristan N., Bunker, Andrew J., Egami, Eiichi, Maseda, Michael V., Tacchella, Sandro, and Willmer, Christopher N. A. 2020. "Simulating JWST/NIRCam Color Selection of High-redshift Galaxies." The Astrophysical Journal 892:125.
ID: 156985
Type: article
Authors: Hainline, Kevin N.; Hviding, Raphael E.; Rieke, Marcia; Shivaei, Irene; Endsley, Ryan; Curtis-Lake, Emma; Smit, Renske; Williams, Christina C.; Alberts, Stacey; K Boyett, Kristan N.; Bunker, Andrew J.; Egami, Eiichi; Maseda, Michael V.; Tacchella, Sandro; Willmer, Christopher N. A.
Abstract: The Near Infrared Camera (NIRCam) instrument on the upcoming James Webb Space Telescope will offer an unprecedented view of the most distant galaxies. In preparation for future deep NIRCam extragalactic surveys, it is crucial to understand the color selection of high-redshift galaxies using the Lyman dropout technique. To that end, we have used the JAdes extraGalactic Ultradeep Artificial Realizations mock catalog to simulate a series of extragalactic surveys with realistic noise estimates. This enables us to explore different color selections and their impact on the number density of recovered high-redshift galaxies and lower-redshift interlopers. We explore how survey depth, detection signal-to-noise ratio, color selection method, detection filter choice, and the presence of the Lyα emission line affects the resulting dropout selected samples. We find that redder selection colors reduce the number of recovered high-redshift galaxies, but the overall accuracy of the final sample is higher. In addition, we find that methods that utilize two or three color cuts have higher accuracy because of their ability to select against low-redshift quiescent and faint dusty interloper galaxies. We also explore the near-IR colors of brown dwarfs and demonstrate that, while they are predicted to have low on-sky densities, they are most likely to be recovered in F090W dropout selection, but there are color cuts that help to mitigate this contamination. Overall, our results provide NIRCam selection methods to aid in the creation of large, pure samples of ultra-high-redshift galaxies from photometry alone.
The diversity and variability of star formation histories in models of galaxy evolutionIyer, Kartheik G.Tacchella, SandroGenel, ShyHayward, Christopher C.Hernquist, LarsBrooks, Alyson M.Caplar, NevenDavé, RomeelDiemer, BenediktForbes, John C.Gawiser, EricSomerville, Rachel S.Starkenburg, Tjitske K.DOI: info:10.1093/mnras/staa2150v. 498430–463
Iyer, Kartheik G., Tacchella, Sandro, Genel, Shy, Hayward, Christopher C., Hernquist, Lars, Brooks, Alyson M., Caplar, Neven, Davé, Romeel, Diemer, Benedikt, Forbes, John C., Gawiser, Eric, Somerville, Rachel S., and Starkenburg, Tjitske K. 2020. "The diversity and variability of star formation histories in models of galaxy evolution." Monthly Notices of the Royal Astronomical Society 498:430– 463.
ID: 158032
Type: article
Authors: Iyer, Kartheik G.; Tacchella, Sandro; Genel, Shy; Hayward, Christopher C.; Hernquist, Lars; Brooks, Alyson M.; Caplar, Neven; Davé, Romeel; Diemer, Benedikt; Forbes, John C.; Gawiser, Eric; Somerville, Rachel S.; Starkenburg, Tjitske K.
Abstract: Understanding the variability of galaxy star formation histories (SFHs) across a range of time-scales provides insight into the underlying physical processes that regulate star formation within galaxies. We compile the SFHs of galaxies at z = 0 from an extensive set of models, ranging from cosmological hydrodynamical simulations (Illustris, IllustrisTNG, Mufasa, Simba, EAGLE), zoom simulations (FIRE-2, g14, and Marvel/Justice League), semi-analytic models (Santa Cruz SAM) and empirical models (UniverseMachine), and quantify the variability of these SFHs on different time-scales using the power spectral density (PSD) formalism. We find that the PSDs are well described by broken power laws, and variability on long time-scales (≳1 Gyr) accounts for most of the power in galaxy SFHs. Most hydrodynamical models show increased variability on shorter time-scales (≲300 Myr) with decreasing stellar mass. Quenching can induce ∼0.4-1 dex of additional power on time-scales >1 Gyr. The dark matter accretion histories of galaxies have remarkably self-similar PSDs and are coherent with the in situ star formation on time-scales >3 Gyr. There is considerable diversity among the different models in their (i) power due to star formation rate variability at a given time-scale, (ii) amount of correlation with adjacent time-scales (PSD slope), (iii) evolution of median PSDs with stellar mass, and (iv) presence and locations of breaks in the PSDs. The PSD framework is a useful space to study the SFHs of galaxies since model predictions vary widely. Observational constraints in this space will help constrain the relative strengths of the physical processes responsible for this variability.
A panchromatic spatially resolved analysis of nearby galaxies - II. The main sequence - gas relation at sub-kpc scale in grand-design spiralsMorselli, L.Rodighiero, G.Enia, A.Corbelli, E.Casasola, V.Rodríguez-Muñoz, L.Renzini, A.Tacchella, SandroBaronchelli, I.Bianchi, S.Cassata, P.Franceschini, A.Mancini, C.Negrello, M.Popesso, P.Romano, M.DOI: info:10.1093/mnras/staa1811v. 4964606–4623
Morselli, L., Rodighiero, G., Enia, A., Corbelli, E., Casasola, V., Rodríguez-Muñoz, L., Renzini, A., Tacchella, Sandro, Baronchelli, I., Bianchi, S., Cassata, P., Franceschini, A., Mancini, C., Negrello, M., Popesso, P., and Romano, M. 2020. "A panchromatic spatially resolved analysis of nearby galaxies - II. The main sequence - gas relation at sub-kpc scale in grand-design spirals." Monthly Notices of the Royal Astronomical Society 496:4606– 4623.
ID: 157845
Type: article
Authors: Morselli, L.; Rodighiero, G.; Enia, A.; Corbelli, E.; Casasola, V.; Rodríguez-Muñoz, L.; Renzini, A.; Tacchella, Sandro; Baronchelli, I.; Bianchi, S.; Cassata, P.; Franceschini, A.; Mancini, C.; Negrello, M.; Popesso, P.; Romano, M.
Abstract: In this work, we analyse the connection between gas availability and the position of a region with respect to the spatially resolved main-sequence (MS) relation. Following the procedure presented in Enia et al. (2020), for a sample of five face-on, grand design spiral galaxies located on the MS we obtain estimates of stellar mass and star formation rate surface densities (Σ and ΣSFR) within cells of 500 pc size. Thanks to H I 21cm and 12CO(2-1) maps of comparable resolution, within the same cells we estimate the surface densities of the atomic (ΣH I) and molecular ( $\Sigma _{\rm {H_2}}$ ) gas and explore the correlations among all these quantities. Σ, ΣSFR, and $\Sigma _{\rm {H_2}}$ define a 3D relation whose projections are the spatially resolved MS, the Kennicutt-Schmidt law and the molecular gas MS. We find that $\Sigma _{\rm {H_2}}$ steadily increases along the MS relation and is almost constant perpendicular to it. ΣH I is nearly constant along the MS and increases in its upper envelope. As a result, ΣSFR can be expressed as a function of Σ and ΣH I, following the relation log ΣSFR = 0.97log Σ + 1.99log ΣH I - 11.11. We show that the total gas fraction significantly increases towards the starburst regions, accompanied by a weak increase in star formation efficiency. Finally, we find that H2/H I varies strongly with the distance from the MS, dropping dramatically in regions of intense star formation, where the UV radiation from newly formed stars dissociates the H2 molecule, illustrating the self-regulating nature of the star formation process.
Galaxy Sizes Since z = 2 from the Perspective of Stellar Mass Distribution within GalaxiesMosleh, MoeinHosseinnejad, ShivaHosseini-ShahiSavandi, S. ZahraTacchella, SandroDOI: info:10.3847/1538-4357/abc7ccv. 905170
Mosleh, Moein, Hosseinnejad, Shiva, Hosseini-ShahiSavandi, S. Zahra, and Tacchella, Sandro. 2020. "Galaxy Sizes Since z = 2 from the Perspective of Stellar Mass Distribution within Galaxies." The Astrophysical Journal 905:170.
ID: 158659
Type: article
Authors: Mosleh, Moein; Hosseinnejad, Shiva; Hosseini-ShahiSavandi, S. Zahra; Tacchella, Sandro
Abstract: How stellar mass assembles within galaxies is still an open question. We present measurements of the stellar mass distribution on kiloparsec-scales for ˜5500 galaxies with stellar masses above $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 9.8$ up to redshift 2.0. We create stellar mass maps from Hubble Space Telescope observations by means of the pixel-by-pixel spectral energy distribution fitting method. These maps are used to derive radii encompassing 20%, 50%, and 80% (r20, r50, and r80) of the total stellar mass from the best-fit Sérsic models. The reliability and limitations of the structural parameter measurements are checked extensively using a large sample (˜3000) of simulated galaxies. The size-mass relations and redshift evolution of r20, r50, and r80 are explored for star-forming and quiescent galaxies. At fixed mass, the star-forming galaxies do not show significant changes in their r20, r50, and r80 sizes, indicating self-similar growth. Only above the pivot stellar mass of $\mathrm{log}({M}_{* }/{M}_{\odot })\simeq 10.5$ does r80 evolve as r80 ? (1 + z)-0.85±0.20, indicating that mass builds up in the outskirts of these systems (inside-out growth). The Sérsic values also increase for the massive star-forming galaxies toward late cosmic time. Massive quiescent galaxies show stronger size evolution at all radii, in particular, the r20 sizes. For these massive galaxies, Sérsic values remain almost constant since at least z ˜ 1.3, indicating that the strong size evolution is related to the changes in the outer parts of these galaxies. We make all the structural parameters publicly available.
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape FractionsNaidu, Rohan P.Tacchella, SandroMason, Charlotte A.Bose, SownakOesch, Pascal A.Conroy, CharlieDOI: info:10.3847/1538-4357/ab7cc9v. 892109
Naidu, Rohan P., Tacchella, Sandro, Mason, Charlotte A., Bose, Sownak, Oesch, Pascal A., and Conroy, Charlie. 2020. "Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions." The Astrophysical Journal 892:109.
ID: 157130
Type: article
Authors: Naidu, Rohan P.; Tacchella, Sandro; Mason, Charlotte A.; Bose, Sownak; Oesch, Pascal A.; Conroy, Charlie
Abstract: The protagonists of the last great phase transition of the universe - cosmic reionization - remain elusive. Faint star-forming galaxies are leading candidates because they are found to be numerous and may have significant ionizing photon escape fractions (fesc). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density (ρSFR at z > 8). We generate an ionizing spectrum for each galaxy in our model and constrain fesc by leveraging latest measurements of the reionization timeline (e.g., Lyα damping of quasars and galaxies at z > 7). Assuming a constant fesc across all sources at z > 6, we find MUV esc = 0.21-0.04+0.06 to complete reionization. The inferred Intergalactic Medium neutral fraction is [0.9, 0.5, 0.1] at z=[8.2,6.8,6.2] ± 0.2 - that is, the bulk of reionization transpires rapidly in 300 Myr, driven by the z > 8 ρSFR and favored by high neutral fractions (∼60%-90%) measured at z ∼ 7-8. Inspired by the emergent sample of Lyman Continuum (LyC) leakers spanning z ∼ 0-6.6 that overwhelmingly displays higher- than-average star-formation surface density (ΣSFR), we propose a physically motivated model relating fesc to ΣSFR and find fesc ∝ ΣSFR0.4±0.1. Since ΣSFR falls by ∼2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on fesc at lower redshifts and its required evolution to fesc ∼ 0.2 at z > 6. Within this model, strikingly, ∼ 0.2 at z > 6. Within this model, strikingly, UV /M) > 8 (the "oligarchs") account for ≳80% of the reionization budget - a stark departure from the canonical "democratic" reionization led by copious faint sources. In fact, faint sources (MUV > -16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7-8. Shallow faint-end slopes of the UV luminosity function (αUV > -2) and/or fesc distributions skewed toward massive galaxies produce the required late and rapid reionization. We predict that LyC leakers like COLA1 (z = 6.6, fesc ∼ 30%, MUV = -21.5) will become increasingly common toward z ∼ 6 and that the drivers of reionization do not lie hidden across the faint end of the luminosity function but are already known to us.
CANDELS Meets GSWLC: Evolution of the Relationship between Morphology and Star Formation Since z = 2Osborne, ChandlerSalim, SamirDamjanov, IvanaFaber, S. M.Huertas-Company, MarcKoo, David C.Mantha, Kameswara BharadwajMcIntosh, Daniel H.Primack, Joel R.Tacchella, SandroDOI: info:10.3847/1538-4357/abb5afv. 90277
Osborne, Chandler, Salim, Samir, Damjanov, Ivana, Faber, S. M., Huertas-Company, Marc, Koo, David C., Mantha, Kameswara Bharadwaj, McIntosh, Daniel H., Primack, Joel R., and Tacchella, Sandro. 2020. "CANDELS Meets GSWLC: Evolution of the Relationship between Morphology and Star Formation Since z = 2." The Astrophysical Journal 902:77.
ID: 158815
Type: article
Authors: Osborne, Chandler; Salim, Samir; Damjanov, Ivana; Faber, S. M.; Huertas-Company, Marc; Koo, David C.; Mantha, Kameswara Bharadwaj; McIntosh, Daniel H.; Primack, Joel R.; Tacchella, Sandro
Abstract: Galaxy morphology and its evolution over the cosmic epoch hold important clues for understanding the regulation of star formation (SF). However, studying the relationship between morphology and SF has been hindered by the availability of consistent data at different redshifts. Our sample, combining CANDELS (0.8 < z < 2.5) and the GALEX-SDSS-WISE Legacy Catalog (GSWLC; z ˜ 0), has physical parameters derived using consistent SED fitting with flexible dust attenuation laws. We adopt visual classifications from Kartaltepe et al. and expand them to z ˜ 0 using SDSS images matching the physical resolution of CANDELS rest-frame optical images and deep FUV GALEX images matching the physical resolution of the CANDELS rest-frame FUV images. Our main finding is that disks with SF clumps at z ˜ 0 make a similar fraction (˜15%) of star-forming galaxies as at z ˜ 2. The clumpy disk contribution to the SF budget peaks at z ˜ 1, rather than z ˜ 2, suggesting that the principal epoch of disk assembly continues to lower redshifts. Star-forming spheroids ("blue nuggets"), though less centrally concentrated than quenched spheroids, contribute significantly (˜15%) to the SF budget at z ˜ 1-2, suggesting that compaction precedes quenching. Among green valley and quiescent galaxies, the pure spheroid fraction drops after z ˜ 1, whereas spheroids with disks (S0-like) become dominant. Mergers at or nearing coalescence are enhanced in SFR relative to the main sequence at all redshifts by a factor of ˜2, but contribute ?5% to the SF budget, with their contribution remaining small above the main sequence.
High-redshift JWST predictions from IllustrisTNG: II. Galaxy line and continuum spectral indices and dust attenuation curvesShen, XuejianVogelsberger, MarkNelson, DylanPillepich, AnnalisaTacchella, SandroMarinacci, FedericoTorrey, PaulHernquist, LarsSpringel, VolkerDOI: info:10.1093/mnras/staa1423v. 4954747–4768
Shen, Xuejian, Vogelsberger, Mark, Nelson, Dylan, Pillepich, Annalisa, Tacchella, Sandro, Marinacci, Federico, Torrey, Paul, Hernquist, Lars, and Springel, Volker. 2020. "High-redshift JWST predictions from IllustrisTNG: II. Galaxy line and continuum spectral indices and dust attenuation curves." Monthly Notices of the Royal Astronomical Society 495:4747– 4768.
ID: 156891
Type: article
Authors: Shen, Xuejian; Vogelsberger, Mark; Nelson, Dylan; Pillepich, Annalisa; Tacchella, Sandro; Marinacci, Federico; Torrey, Paul; Hernquist, Lars; Springel, Volker
Abstract: We present predictions for high redshift (z = 2-10) galaxy populations based on the IllustrisTNG simulation suite and a full Monte Carlo dust radiative transfer post-processing. Specifically, we discuss the H α and H β + $[\rm O \,{\small III}]$ luminosity functions up to z = 8. The predicted H β + $[\rm O \,{\small III}]$ luminosity functions are consistent with present observations at z ≲ 3 with ${\lesssim} 0.1\, {\rm dex}$ differences in luminosities. However, the predicted H α luminosity function is ${\sim }0.3\, {\rm dex}$ dimmer than the observed one at z ≃ 2. Furthermore, we explore continuum spectral indices, the Balmer break at 4000 Å; (D4000) and the UV continuum slope β. The median D4000 versus specific star formation rate relation predicted at z = 2 is in agreement with the local calibration despite a different distribution pattern of galaxies in this plane. In addition, we reproduce the observed AUV versus β relation and explore its dependence on galaxy stellar mass, providing an explanation for the observed complexity of this relation. We also find a deficiency in heavily attenuated, UV red galaxies in the simulations. Finally, we provide predictions for the dust attenuation curves of galaxies at z = 2-6 and investigate their dependence on galaxy colours and stellar masses. The attenuation curves are steeper in galaxies at higher redshifts, with bluer colours, or with lower stellar masses. We attribute these predicted trends to dust geometry. Overall, our results are consistent with present observations of high-redshift galaxies. Future James Webb Space Telecope observations will further test these predictions.
Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflowTacchella, SandroForbes, John C.Caplar, NevenDOI: info:10.1093/mnras/staa1838v. 497698–725
Tacchella, Sandro, Forbes, John C., and Caplar, Neven. 2020. "Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflow." Monthly Notices of the Royal Astronomical Society 497:698– 725.
ID: 157843
Type: article
Authors: Tacchella, Sandro; Forbes, John C.; Caplar, Neven
Abstract: A key uncertainty in galaxy evolution is the physics regulating star formation, ranging from small-scale processes related to the life-cycle of molecular clouds within galaxies to large-scale processes such as gas accretion on to galaxies. We study the imprint of such processes on the time-variability of star formation with an analytical approach tracking the gas mass of galaxies ('regulator model'). Specifically, we quantify the strength of the fluctuation in the star-formation rate (SFR) on different time-scales, i.e. the power spectral density (PSD) of the star-formation history, and connect it to gas inflow and the life-cycle of molecular clouds. We show that in the general case the PSD of the SFR has three breaks, corresponding to the correlation time of the inflow rate, the equilibrium time-scale of the gas reservoir of the galaxy, and the average lifetime of individual molecular clouds. On long and intermediate time-scales (relative to the dynamical time-scale of the galaxy), the PSD is typically set by the variability of the inflow rate and the interplay between outflows and gas depletion. On short time-scales, the PSD shows an additional component related to the life-cycle of molecular clouds, which can be described by a damped random walk with a power-law slope of β ≍ 2 at high frequencies with a break near the average cloud lifetime. We discuss star-formation 'burstiness' in a wide range of galaxy regimes, study the evolution of galaxies about the main sequence ridgeline, and explore the applicability of our method for understanding the star-formation process on cloud-scale from galaxy-integrated measurements.
High-redshift JWST predictions from IllustrisTNG: dust modelling and galaxy luminosity functionsVogelsberger, MarkNelson, DylanPillepich, AnnalisaShen, XuejianMarinacci, FedericoSpringel, VolkerPakmor, RüdigerTacchella, SandroWeinberger, RainerTorrey, PaulHernquist, LarsDOI: info:10.1093/mnras/staa137v. 4925167–5201
Vogelsberger, Mark, Nelson, Dylan, Pillepich, Annalisa, Shen, Xuejian, Marinacci, Federico, Springel, Volker, Pakmor, Rüdiger, Tacchella, Sandro, Weinberger, Rainer, Torrey, Paul, and Hernquist, Lars. 2020. "High-redshift JWST predictions from IllustrisTNG: dust modelling and galaxy luminosity functions." Monthly Notices of the Royal Astronomical Society 492:5167– 5201.
ID: 156459
Type: article
Authors: Vogelsberger, Mark; Nelson, Dylan; Pillepich, Annalisa; Shen, Xuejian; Marinacci, Federico; Springel, Volker; Pakmor, Rüdiger; Tacchella, Sandro; Weinberger, Rainer; Torrey, Paul; Hernquist, Lars
Abstract: The James Webb Space Telescope (JWST) promises to revolutionize our understanding of the early Universe, and contrasting its upcoming observations with predictions of the Λ cold dark matter model requires detailed theoretical forecasts. Here, we exploit the large dynamic range of the IllustrisTNG simulation suite, TNG50, TNG100, and TNG300, to derive multiband galaxy luminosity functions from z = 2 to z = 10. We put particular emphasis on the exploration of different dust attenuation models to determine galaxy luminosity functions for the rest-frame ultraviolet (UV), and apparent wide NIRCam bands. Our most detailed dust model is based on continuum Monte Carlo radiative transfer calculations employing observationally calibrated dust properties. This calibration results in constraints on the redshift evolution of the dust attenuation normalization and dust-to-metal ratios yielding a stronger redshift evolution of the attenuation normalization compared to most previous theoretical studies. Overall we find good agreement between the rest- frame UV luminosity functions and observational data for all redshifts, also beyond the regimes used for the dust model calibrations. Furthermore, we also recover the observed high-redshift (z = 4-6) UV luminosity versus stellar mass relation, the H α versus star formation rate relation, and the H α luminosity function at z = 2. The bright end (MUV > -19.5) cumulative galaxy number densities are consistent with observational data. For the F200W NIRCam band, we predict that JWST will detect ∼80 (∼200) galaxies with a signal-to-noise ratio of 10 (5) within the NIRCam field of view, 2.2× 2.2 arcmin2, for a total exposure time of 10^5 s in the redshift range z = 8 ± 0.5. These numbers drop to ∼10 (∼40) for an exposure time of 10^4 s.
Photometric properties of reionization-epoch galaxies in the SIMBA simulationsWu, XiaohanDavé, RomeelTacchella, SandroLotz, JenniferDOI: info:10.1093/mnras/staa1044v. 4945636–5651
Wu, Xiaohan, Davé, Romeel, Tacchella, Sandro, and Lotz, Jennifer. 2020. "Photometric properties of reionization-epoch galaxies in the SIMBA simulations." Monthly Notices of the Royal Astronomical Society 494:5636– 5651.
ID: 157844
Type: article
Authors: Wu, Xiaohan; Davé, Romeel; Tacchella, Sandro; Lotz, Jennifer
Abstract: We study the photometric properties and sizes of the reionization-epoch galaxies in high-resolution SIMBA cosmological hydrodynamical simulations with box sizes of $[25,50]\, h^{-1}\, {\rm Mpc}$ . Assuming various attenuation laws, we compute photometry by extincting each star particle's spectrum using the line-of-sight gas metal column density. The predicted ultraviolet luminosity function (UVLF) generally agrees with observations at z = 6, owing to a partial cancellation between the high metallicities of the simulated galaxies and lower dust-to-metal ratios. The simulated z = 8 UVLF is low compared to observations, likely owing to excessive dust extinction. SIMBA predicts UV continuum slopes (β) in agreement with the z = 6 observations, with the best agreement obtained using a Calzetti extinction law. Interestingly, the gas-phase mass-metallicity relation in SIMBA is higher at z ∼ 6 than at z ∼ 2, suggesting that rapid early enrichment (and dust growth) might be necessary to match the observed β. We find that β is more sensitive to the dust extinction law than the UVLF. By generating mock James Webb Space Telescope (JWST) images and analysing in a manner similar to observations, we show that SIMBA's galaxy size-luminosity relation well reproduces the current z = 6 Hubble observations. Unlike observations at lower redshifts, SIMBA predicts similar rest-UV and rest-optical sizes of z = 6 galaxies, owing to weak age gradients and dust extinction in star-forming regions counteract each other to weaken the colour gradients within galaxies. These predictions will be testable with JWST.
Stochastic modelling of star-formation histories I: the scatter of the star-forming main sequenceCaplar, NevenTacchella, SandroDOI: info:10.1093/mnras/stz1449v. 4873845–3869
Caplar, Neven and Tacchella, Sandro. 2019. "Stochastic modelling of star-formation histories I: the scatter of the star-forming main sequence." Monthly Notices of the Royal Astronomical Society 487:3845– 3869.
ID: 154270
Type: article
Authors: Caplar, Neven; Tacchella, Sandro
Abstract: We present a framework for modelling the star-formation histories of galaxies as a stochastic process. We define this stochastic process through a power spectrum density with a functional form of a broken power law. Star-formation histories are correlated on short time-scales, the strength of this correlation described by a power-law slope, α, and they decorrelate to resemble white noise over a time-scale that is proportional to the time-scale of the break in the power spectrum density, τbreak. We use this framework to explore the properties of the stochastic process that, we assume, gives rise to the log-normal scatter about the relationship between star-formation rate and stellar mass, the so-called galaxy star-forming main sequence. Specifically, we show how the measurements of the normalization and width (σMS) of the main sequence, measured in several passbands that probe different time-scales, give a constraint on the parameters of the underlying power spectrum density. We first derive these results analytically for a simplified case where we model observations by averaging over the recent star-formation history. We then run numerical simulations to find results for more realistic observational cases. As a proof of concept, we use observational estimates of the main sequence scatter at z ̃ 0 and M ≈ 1010 M measured in H α, UV+IR, and the u-band. The result is degenerate in the τbreak-α space, but if we assume α = 2, we measure \tau _break=170^{+169}_{-85} Myr. This implies that star-formation histories of galaxies lose `memory' of their previous activity on a time-scale of ̃200 Myr.
Kiloparsec Scale Properties of Star Formation Driven Outflows at z ̃ 2.3 in the SINS/zC-SINF AO SurveyDavies, R. L.Förster Schreiber, N. M.Übler, H.Genzel, R.Lutz, D.Renzini, A.Tacchella, SandroTacconi, L. J.Belli, S.Burkert, A.Carollo, C. M.Davies, R. I.Herrera-Camus, R.Lilly, S. J.Mancini, C.Naab, T.Nelson, Erica J.Price, S. H.Shimizu, T. T.Sternberg, A.Wisnioski, E.Wuyts, S.DOI: info:10.3847/1538-4357/ab06f1v. 873122
Davies, R. L., Förster Schreiber, N. M., Übler, H., Genzel, R., Lutz, D., Renzini, A., Tacchella, Sandro, Tacconi, L. J., Belli, S., Burkert, A., Carollo, C. M., Davies, R. I., Herrera-Camus, R., Lilly, S. J., Mancini, C., Naab, T., Nelson, Erica J., Price, S. H., Shimizu, T. T., Sternberg, A., Wisnioski, E., and Wuyts, S. 2019. "Kiloparsec Scale Properties of Star Formation Driven Outflows at z ̃ 2.3 in the SINS/zC-SINF AO Survey." The Astrophysical Journal 873:122.
ID: 155413
Type: article
Authors: Davies, R. L.; Förster Schreiber, N. M.; Übler, H.; Genzel, R.; Lutz, D.; Renzini, A.; Tacchella, Sandro; Tacconi, L. J.; Belli, S.; Burkert, A.; Carollo, C. M.; Davies, R. I.; Herrera-Camus, R.; Lilly, S. J.; Mancini, C.; Naab, T.; Nelson, Erica J.; Price, S. H.; Shimizu, T. T.; Sternberg, A.; Wisnioski, E.; Wuyts, S.
Abstract: We investigate the relationship between star formation activity and outflow properties on kiloparsec scales in a sample of 28 star-forming galaxies at z ̃ 2-2.6, using adaptive optics assisted integral field observations from SINFONI on the Very Large Telescope. The narrow and broad components of the Hα emission are used to simultaneously determine the local star formation rate surface density ({{{Σ }}}SFR}), and the outflow velocity {v}out} and mass outflow rate {\dot{M}}out}, respectively. We find clear evidence for faster outflows with larger mass loading factors at higher {{{Σ }}}SFR}. The outflow velocities scale as {v}out} ∝ {{{Σ }}}SFR} 0.34±0.10, which suggests that the outflows may be driven by a combination of mechanical energy released by supernova explosions and stellar winds, as well as radiation pressure acting on dust grains. The majority of the outflowing material does not have sufficient velocity to escape from the galaxy halos, but will likely be re-accreted and contribute to the chemical enrichment of the galaxies. In the highest {{{Σ }}}SFR} regions the outflow component contains an average of ̃45% of the Hα flux, while in the lower {{{Σ }}}SFR} regions only ̃10% of the Hα flux is associated with outflows. The mass loading factor, η = {\dot{M}}out}/SFR, is positively correlated with {{{Σ }}}SFR} but is relatively low even at the highest {{{Σ }}}SFR}: η ≲ 0.5 × (380 cm-3/n e ). This may be in tension with the η ≳ 1 required by cosmological simulations, unless a significant fraction of the outflowing mass is in other gas phases and has sufficient velocity to escape the galaxy halos. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO Programme IDs 075.A-0466, 079.A-0341, 080.A-0330, 080.A-0339, 080.A-0635, 081.A-0672, 081.B-0568, 183.A-0781, 087.A-0081, and 088.A-0209.
Atomic and molecular gas in IllustrisTNG galaxies at low redshiftDiemer, BenediktStevens, Adam R. H.Lagos, Claudia del P.Calette, A. R.Tacchella, SandroHernquist, LarsMarinacci, FedericoNelson, DylanPillepich, AnnalisaRodriguez-Gomez, VicenteVillaescusa-Navarro, FranciscoVogelsberger, MarkDOI: info:10.1093/mnras/stz1323v. 4871529–1550
Diemer, Benedikt, Stevens, Adam R. H., Lagos, Claudia del P., Calette, A. R., Tacchella, Sandro, Hernquist, Lars, Marinacci, Federico, Nelson, Dylan, Pillepich, Annalisa, Rodriguez-Gomez, Vicente, Villaescusa-Navarro, Francisco, and Vogelsberger, Mark. 2019. "Atomic and molecular gas in IllustrisTNG galaxies at low redshift." Monthly Notices of the Royal Astronomical Society 487:1529– 1550.
ID: 154280
Type: article
Authors: Diemer, Benedikt; Stevens, Adam R. H.; Lagos, Claudia del P.; Calette, A. R.; Tacchella, Sandro; Hernquist, Lars; Marinacci, Federico; Nelson, Dylan; Pillepich, Annalisa; Rodriguez-Gomez, Vicente; Villaescusa-Navarro, Francisco; Vogelsberger, Mark
Abstract: We have recently developed a post-processing framework to estimate the abundance of atomic and molecular hydrogen (H I and H2, respectively) in galaxies in large-volume cosmological simulations. Here we compare the H I and H2 content of IllustrisTNG galaxies to observations. We mostly restrict this comparison to z ≈ 0 and consider six observational metrics: the overall abundance of H I and H2, their mass functions, gas fractions as a function of stellar mass, the correlation between H2 and star formation rate, the spatial distribution of gas, and the correlation between gas content and morphology. We find generally good agreement between simulations and observations, particularly for the gas fractions and the H I mass-size relation. The H2 mass correlates with star formation rate as expected, revealing an almost constant depletion time that evolves up to z = 2 as observed. However, we also discover a number of tensions with varying degrees of significance, including an overestimate of the total neutral gas abundance at z = 0 by about a factor of 2 and a possible excess of satellites with no or very little neutral gas. These conclusions are robust to the modelling of the H I/H2 transition. In terms of their neutral gas properties, the IllustrisTNG simulations represent an enormous improvement over the original Illustris run. All data used in this paper are publicly available as part of the IllustrisTNG data release.
The MUSE Atlas of Disks (MAD): resolving star formation rates and gas metallicities on <100 pc scales†Erroz-Ferrer, SantiagoCarollo, C. Marcelladen Brok, MarkOnodera, MasatoBrinchmann, JarleMarino, Raffaella A.Monreal-Ibero, AnaSchaye, JoopWoo, JoannaCibinel, AnnaDebattista, Victor P.Inami, HanaeMaseda, MichaelRichard, JohanTacchella, SandroWisotzki, LutzDOI: info:10.1093/mnras/stz194v. 4845009–5027
Erroz-Ferrer, Santiago, Carollo, C. Marcella, den Brok, Mark, Onodera, Masato, Brinchmann, Jarle, Marino, Raffaella A., Monreal-Ibero, Ana, Schaye, Joop, Woo, Joanna, Cibinel, Anna, Debattista, Victor P., Inami, Hanae, Maseda, Michael, Richard, Johan, Tacchella, Sandro, and Wisotzki, Lutz. 2019. "The MUSE Atlas of Disks (MAD): resolving star formation rates and gas metallicities on <100 pc scales†." Monthly Notices of the Royal Astronomical Society 484:5009– 5027.
ID: 151202
Type: article
Authors: Erroz-Ferrer, Santiago; Carollo, C. Marcella; den Brok, Mark; Onodera, Masato; Brinchmann, Jarle; Marino, Raffaella A.; Monreal-Ibero, Ana; Schaye, Joop; Woo, Joanna; Cibinel, Anna; Debattista, Victor P.; Inami, Hanae; Maseda, Michael; Richard, Johan; Tacchella, Sandro; Wisotzki, Lutz
Abstract: We study the physical properties of the ionized gas in local discs using the sample of 38 nearby ˜108.5-11.2 M Star-Forming Main-Sequence (SFMS) galaxies observed so far as part of the MUSE Atlas of Disks (MAD). Specifically, we use all strong emission lines in the MUSE wavelength range 4650-9300 Å to investigate the resolved ionized gas properties on ˜100 pc scales. This spatial resolution enables us to disentangle H II regions from the diffuse ionized gas (DIG) in the computation of gas metallicities and star formation rates (SFRs) of star-forming regions. The gas metallicities generally decrease with radius. The metallicity of the H II regions is on average ˜0.1 dex higher than that of the DIG, but the metallicity radial gradient in both components is similar. The mean metallicities within the inner galaxy cores correlate with the total stellar mass of the galaxies. On our < 100 pc scales, we find two correlations previously reported at kpc scales: a spatially resolved mass-metallicity relation (RMZR) and a spatially resolved SFMS (RSFMS). We find no secondary dependence of the RMZR with the SFR density. We find that both resolved relations have a local origin, as they do not depend on the total stellar mass. The observational results of this paper are consistent with the inside-out scenario for the growth of galactic disks.
The Recent Burstiness of Star Formation in Galaxies at z ̃ 4.5 from Hα MeasurementsFaisst, Andreas L.Capak, Peter L.Emami, NajmehTacchella, SandroLarson, Kirsten L.DOI: info:10.3847/1538-4357/ab425bv. 884133
Faisst, Andreas L., Capak, Peter L., Emami, Najmeh, Tacchella, Sandro, and Larson, Kirsten L. 2019. "The Recent Burstiness of Star Formation in Galaxies at z ̃ 4.5 from Hα Measurements." The Astrophysical Journal 884:133.
ID: 154642
Type: article
Authors: Faisst, Andreas L.; Capak, Peter L.; Emami, Najmeh; Tacchella, Sandro; Larson, Kirsten L.
Abstract: The redshift range z = 4-6 marks a transition phase between primordial and mature galaxy formation in which galaxies considerably increase their stellar mass, metallicity, and dust content. The study of galaxies in this redshift range is therefore important to understanding early galaxy formation and the fate of galaxies at later times. Here, we investigate the burstiness of the recent star formation history (SFH) of 221z ̃ 4.5 main-sequence galaxies at {log}(M/{M})> 9.7 by comparing their ultra-violet (UV) continuum, Hα luminosity, and Hα equivalent-width (EW). The Hα properties are derived from the Spitzer [3.6 μm]-[4.5 μm] broadband color, thereby properly taking into account model and photometric uncertainties. We find a significant scatter between Hα- and UV-derived luminosities and star formation rates (SFRs). About half of the galaxies show a significant excess in Hα compared to expectations from a constant smooth SFH. We also find a tentative anticorrelation between Hα EW and stellar mass, ranging from 1000 Å at {log}(M/{M})))> 11. Consulting models suggests that most z ̃ 4.5 galaxies had a burst of star formation within the last 50 Myr, increasing their SFRs by a factor of >5. The most massive galaxies on the other hand might decrease their SFRs and may be transitioning to a quiescent stage by z = 4. We identify differential dust attenuation (f) between stars and nebular regions as the main contributor to the uncertainty. With local galaxies selected by increasing Hα EW (reaching values similar to high-z galaxies), we predict that f approaches unity at z > 4, consistent with the extrapolation of measurements out to z = 2.
Beyond UVJ: More Efficient Selection of Quiescent Galaxies with Ultraviolet/Mid-infrared FluxesLeja, JoelTacchella, SandroConroy, CharlieDOI: info:10.3847/2041-8213/ab2f8cv. 880L9
Leja, Joel, Tacchella, Sandro, and Conroy, Charlie. 2019. "Beyond UVJ: More Efficient Selection of Quiescent Galaxies with Ultraviolet/Mid-infrared Fluxes." The Astrophysical Journal 880:L9.
ID: 154164
Type: article
Authors: Leja, Joel; Tacchella, Sandro; Conroy, Charlie
Abstract: The UVJ color-color diagram is a popular and efficient method to distinguish between quiescent and star-forming galaxies through their rest-frame U-V versus V-J colors. Here we explore the information content of this color-color space using the Bayesian inference machine Prospector. We fit the same physical model to two data sets: (i) UVJ fluxes alone, and (ii) full UV-mid IR (MIR) broadband spectral energy distributions from the 3D-HST survey. Notably this model uses both nonparametric star formation histories and a flexible dust attenuation curve, both of which have the potential to "break" the typical correlations observed in UVJ color-color space. Instead, these fits confirm observed trends between UVJ colors and observed galaxy properties, including specific star formation rate (sSFR), dust attenuation, stellar age, and stellar metallicity. They also demonstrate that UVJ colors do not, on their own, constrain stellar age or metallicity; the observed trends in the UVJ diagram are instead driven by galaxy scaling relationships and thus will evolve with cosmological time. We also show that UVJ colors "saturate" below {log}({sSFR}/{yr}}-1)≲ -10.5, i.e., changing sSFR no longer produces substantial changes in UVJ colors. We show that far-UV and/or MIR fluxes continue to correlate with sSFR down to low sSFRs and can be used in color-color diagrams to efficiently target galaxies with much lower levels of ongoing star formation. We provide selection criteria in these new color-color spaces as a function of desired sample sSFR.
Model-independent constraints on the hydrogen-ionizing emissivity at z > 6Mason, Charlotte A.Naidu, Rohan P.Tacchella, SandroLeja, JoelDOI: info:10.1093/mnras/stz2291v. 4892669–2676
Mason, Charlotte A., Naidu, Rohan P., Tacchella, Sandro, and Leja, Joel. 2019. "Model-independent constraints on the hydrogen-ionizing emissivity at z > 6." Monthly Notices of the Royal Astronomical Society 489:2669– 2676.
ID: 154621
Type: article
Authors: Mason, Charlotte A.; Naidu, Rohan P.; Tacchella, Sandro; Leja, Joel
Abstract: Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, \dot{N}_\textrm {ion}) at z = 4-14 from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of \dot{N}_\textrm {ion}, allowing us to flexibly explore the entire prior volume. We infer a declining \dot{N}_\textrm {ion} with redshift at z > 6, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the cosmic microwave background (CMB) optical depth and Ly α and Ly β forest dark pixel fraction produce \dot{N}_\textrm {ion} evolution ( d\log _{10}\dot{\mathbf {N}}_{ion}/ dz|_{z=6\rArr 8} = -0.31± 0.35 dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly α damping of galaxies and quasars produces a more rapid decline: d\log _{10}\dot{\mathbf {N}}_{ion}/ dz|_{z=6\rArr 8} =-0.44± 0.22 dex, steeper than the declining galaxy luminosity density (if extrapolated beyond M_UV≳ -13), and constrains the mid-point of reionization to z = 6.93 ± 0.14.