Publication Search Results

ID: 156234
Type: article
Authors: de Menezes, R.; Amaya-Almazán, R. A.; Marchesini, E. J.; Peña-Herazo, H. A.; Massaro, F.; Chavushyan, V.; Paggi, A.; Landoni, M.; Masetti, N.; Ricci, F.; D'Abrusco, Raffaele; La Franca, F.; Smith, Howard A.; Milisavljevic, D.; Tosti, G.; Jiménez-Bailón, E.; Cheung, C. C.
Abstract: The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 γ -ray sources with statistical significance above 4 σ . About 23% of the sources listed in this catalog are unidentified/unassociated γ -ray sources while ∼26% of the sources are classified as blazar candidates of uncertain type (BCUs), lacking optical spectroscopic information. To probe the blazar nature of candidate counterparts of UGSs and BCUs, we started our optical spectroscopic follow up campaign in 2012, which up to date account for more than 350 observed sources. In this paper, the tenth of our campaign, we report on the spectroscopic observations of 37 sources, mostly BCUs, whose observations were carried out predominantly at the Observatorio Astronómico Nacional San Pedro Mártir and the Southern Astrophysical Research Observatory between August 2018 and September 2019. We confirm the BL Lac nature of 27 sources and the flat spectrum radio quasar nature of three sources. The remaining ones are classified as six BL Lacs galaxy-dominated and one normal galaxy. We were also able to measure the redshifts for 20 sources, including 10 BL Lacs. As in previous analyses, the largest fraction of BCUs revealed to be BL Lac objects.

ID: 158825
Type: article
Authors: Jackson, James M.; Allingham, David; Killerby-Smith, Nicholas; Whitaker, J. Scott; Smith, Howard A.; Contreras, Yanett; Guzmán, Andrés E.; Hogge, Taylor; Sanhueza, Patricio; Stephens, Ian W.
Abstract: Because the 157.74 µm [C II] line is the dominant coolant of star-forming regions, it is often used to infer the global star formation rates of galaxies. By characterizing the [C II] and far-infrared emission from nearby Galactic star-forming molecular clumps, it is possible to determine whether extragalactic [C II] emission arises from a large ensemble of such clumps, and whether [C II] is indeed a robust indicator of global star formation. We describe [C II] and far-infrared observations using the FIFI-LS instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) airborne observatory toward four dense, high-mass, Milky Way clumps. Despite similar far-infrared luminosities, the [C II] to far-infrared luminosity ratio, ${L}_{[{\rm{C}}{\rm\small{II}}]}$ /L_FIR, varies by a factor of at least 140 among these four clumps. In particular, for AGAL313.576+0.324, no [C II] line emission is detected despite a FIR luminosity of 24,000 ${L}_{\odot }$ . AGAL313.576+0.324 lies a factor of more than 100 below the empirical correlation curve between ${L}_{[{\rm{C}}{\rm\small{II}}]}$ /L_FIR and ${S}_{\nu }(63\,\mu {\rm{m}})/{S}_{\nu }(158\,\mu {\rm{m}})$ found for galaxies. AGAL313.576+0.324 may be in an early evolutionary "protostellar" phase with insufficient ultraviolet flux to ionize carbon, or in a deeply embedded "'hypercompact" ${\rm{H}}\,{\rm\small{II}}$ region phase where dust attenuation of UV flux limits the region of ionized carbon to undetectably small volumes. Alternatively, its apparent lack of [C II] emission may arise from deep absorption of the [C II] line against the 158 µm continuum, or self-absorption of brighter line emission by foreground material, which might cancel or diminish any emission within the FIFI-LS instrument's broad spectral resolution element ( ${\rm{\Delta }}V\sim 250$ km s^-1).

ID: 157483
Type: article
Authors: Li, Shanghuo; Zhang, Qizhou; Liu, Hauyu Baobab; Beuther, Henrik; Palau, Aina; Girart, Josep Miquel; Smith, Howard A.; Hora, Joseph L.; Lin, Yuxing; Qiu, Keping; Strom, Shaye; Wang, Junzhi; Li, Fei; Yue, Nannan
Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (JVLA) observations of the massive infrared dark cloud NGC 6334S (also known as IRDC G350.56+0.44), located at the southwestern end of the NGC 6334 molecular cloud complex. The H¹³CO⁺ and NH₂D lines covered by the ALMA observations at a ∼3″ angular resolution (∼0.02 pc) reveal that the spatially unresolved nonthermal motions are predominantly subsonic and transonic, a condition analogous to that found in low-mass star-forming molecular clouds. The observed supersonic nonthermal velocity dispersions in massive star-forming regions, often reported in the literature, might be significantly biased by poor spatial resolutions that broaden the observed line widths owing to unresolved motions within the telescope beam. Our 3 mm continuum image resolves 49 dense cores, whose masses range from 0.17 to 14 M_☉. The majority of them are resolved with multiple velocity components. Our analyses of these gas velocity components find an anticorrelation between the gas mass and the virial parameter. This implies that the more massive structures tend to be more gravitationally unstable. Finally, we find that the external pressure in the NGC 6334S cloud is important in confining these dense structures and may play a role in the formation of dense cores and, subsequently, the embedded young stars.

ID: 156820
Type: article
Authors: Mommert, Michael; Hora, Joseph L.; Trilling, David E.; Biver, Nicolas; Wierzchos, Kacper; Harrington Pinto, Olga; Agarwal, Jessica; Kim, Yoonyoung; McNeill, Andrew; Womack, Maria; Knight, Matthew M.; Polishook, David; Moskovitz, Nick; Kelley, Michael S. P.; Smith, Howard A.
Abstract: We report on observations of activity in near-Earth object (3552) Don Quixote using the Spitzer Space Telescope and ground-based telescopes around its 2018 perihelion passage. Spitzer observations obtained six months before perihelion show extended emission around the target's nucleus that is most likely caused by molecular band emission from either CO₂ or CO, but we find no significant emission from dust. Ground-based optical observations taken close to perihelion reveal for the first time activity in the optical wavelengths, which we attribute to solar light reflected from dust particles. IRAM millimeter radio observations taken around the same time are unable to rule out CO as the driver of the molecular band emission observed with Spitzer. The comparison of the gas activity presented here with observations performed during Don Quixote's previous apparition suggests that activity in Don Quixote is recurrent. We conclude that (3552) Don Quixote is most likely a weakly active comet.

ID: 156876
Type: article
Authors: Mommert, Michael; Trilling, David E.; Hora, Joseph L.; Lejoly, Cassandra; Gustafsson, Annika; Knight, Matthew; Moskovitz, Nick; Smith, Howard A.
Abstract: We report on our long-term observational campaign to characterize and monitor a select sample of 75 dynamically selected dormant comet candidates and six near-Sun asteroids. Both asteroid subpopulations can be considered likely to display comet-like activity. Dormant comets are currently inactive comet nuclei that can still harbor volatiles in subsurface layers, whereas near-Sun asteroids have extremely low perihelion distances and are thus prone to catastrophic disruption. As a result of our 4 yr long observing campaign, we find only dormant comet 3552 Don Quixote to show activity during our program. We furthermore find that (51 ± 10)% of dynamically selected dormant comet candidates in near-Earth space have comet-like physical properties, as well as (56 ± 16)% of dynamically selected dormant comet candidates in other parts of the solar system. All of our near-Sun asteroid sample targets are of nonprimitive nature, suggesting that primitive near-Sun asteroids are more likely to disrupt than nonprimitives. We furthermore find a significant fraction of our near-Sun asteroid sample to display extremely blue V-I color indices, potentially hinting at physical alterations of surface material close to the Sun.

ID: 156956
Type: article
Authors: Morford, J. C.; Fenech, D. M.; Prinja, R. K.; Blomme, R.; Yates, J. A.; Drake, J. J.; Eyres, S. P. S.; Richards, A. M. S.; Stevens, I. R.; Wright, N. J.; Clark, J. S.; Dougherty, S.; Pittard, J. M.; Smith, Howard A.; Vink, J. S.
Abstract: Context. The role of massive stars is central to an understanding of galactic ecology. It is important to establish the details of how massive stars provide radiative, chemical, and mechanical feedback in galaxies. Central to these issues is an understanding of the evolution of massive stars, and the critical role of mass loss via strongly structured winds and stellar binarity. Ultimately, and acting collectively, massive stellar clusters shape the structure and energetics of galaxies.
Aims: We aim to conduct high-resolution, deep field mapping at 21 cm of the core of the massive Cygnus OB2 association and to characterise the properties of the massive stars and colliding winds at this waveband.
Methods: We used seven stations of the e-MERLIN radio facility, with its upgraded bandwidth and enhanced sensitivity to conduct a 21 cm census of Cygnus OB2. Based on 42 hours of observations, seven overlapping pointings were employed over multiple epochs during 2014 resulting in 1σ sensitivities down to ∼21 μJy and a resolution of ∼180 mas.
Results: A total of 61 sources are detected at 21 cm over a ∼0.48° × 0.48° region centred on the heart of the Cyg OB2 association. Of these 61 sources, 33 are detected for the first time. We detect a number of previously identified sources including four massive stellar binary systems, two YSOs, and several known X-ray and radio sources. We also detect the LBV candidate (possible binary system) and blue hypergiant star of Cyg OB2 #12.
Conclusions: The 21 cm observations secured in the COBRaS Legacy project provide data to constrain conditions in the outer wind regions of massive stars; determine the non-thermal properties of massive interacting binaries; examine evidence for transient sources, including those associated with young stellar objects; and provide unidentified sources that merit follow-up observations. The 21 cm data are of lasting value and will serve in combination with other key surveys of Cyg OB2, including Chandra and Spitzer.

ID: 158733
Type: article
Authors: Ramos Padilla, Andrés F.; Ashby, M. L. N.; Smith, Howard A.; Martínez-Galarza, Juan R.; Beverage, Aliza G.; Dietrich, Jeremy; Higuera-G., Mario-A; Weiner, Aaron S.
Abstract: Emission from active galactic nuclei (AGNs) is known to play an important role in the evolution of many galaxies including luminous and ultraluminous systems (U/LIRGs), as well as merging systems. However, the extent, duration, and exact effects of its influence are still imperfectly understood. To assess the impact of AGNs on interacting systems, we present a spectral energy distribution (SED) analysis of a sample of 189 nearby galaxies. We gather and systematically re-reduce archival broad-band imaging mosaics from the ultraviolet to the far-infrared using data from GALEX, SDSS, 2MASS, IRAS, WISE, Spitzer, and Herschel. We use spectroscopy from Spitzer/IRS to obtain fluxes from fine-structure lines that trace star formation and AGN activity. Utilizing the SED modelling and fitting tool CIGALE, we derive the physical conditions of the interstellar medium, both in star-forming regions and in nuclear regions dominated by the AGN in these galaxies. We investigate how the star formation rates (SFRs) and the fractional AGN contributions (f_AGN) depend on stellar mass, galaxy type, and merger stage. We find that luminous galaxies more massive than about $10^{10} \,\rm {M}_{*}$ are likely to deviate significantly from the conventional galaxy main-sequence relation. Interestingly, infrared AGN luminosity and stellar mass in this set of objects are much tighter than SFR and stellar mass. We find that buried AGNs may occupy a locus between bright starbursts and pure AGNs in the f_AGN-[Ne V]/[Ne II] plane. We identify a modest correlation between f_AGN and mergers in their later stages.

ID: 151855
Type: article
Authors: D'Abrusco, Raffaele; Álvarez Crespo, Nuria; Massaro, Francesco; Campana, Riccardo; Chavushyan, Vahram; Landoni, Marco; La Franca, Fabio; Masetti, Nicola; Milisavljevic, Dan; Paggi, Alessandro; Ricci, Federica; Smith, Howard A.
Abstract: We present two catalogs of radio-loud candidate blazars whose Wide-Field Infrared Survey Explorer (WISE) mid-infrared colors are selected to be consistent with the colors of confirmed γ-ray-emitting blazars. The first catalog is the improved and expanded release of the WISE Blazar-like Radio-Loud Sources (WIBRaLS) catalog presented by D'Abrusco et al. It includes sources detected in all four WISE filters, spatially cross-matched with radio sources in one of three radio surveys and radio-loud based on their q ₂₂ spectral parameter. WIBRaLS2 includes 9541 sources classified as BL Lacs, flat-spectrum radio quasars, or mixed candidates based on their WISE colors. The second catalog, called KDEBLLACS, based on a new selection technique, contains 5579 candidate BL Lacs extracted from the population of WISE sources detected in the first three WISE passbands ([3.4], [4.6], and [12]) only, whose mid-infrared colors are similar to those of confirmed, γ-ray BL Lacs. Members of KDBLLACS are also required to have a radio counterpart and be radio-loud based on the parameter q ₁₂, defined similarly to the q ₂₂ used for the WIBRaLS2. We describe the properties of these catalogs and compare them with the largest samples of confirmed and candidate blazars in the literature. We cross-match the two new catalogs with the most recent catalogs of γ-ray sources detected by the Fermi Large Area Telescope. Since spectroscopic observations of candidate blazars from the first WIBRaLS catalog within the uncertainty regions of γ-ray unassociated sources confirmed that ∼90% of these candidates are blazars, we anticipate that these new catalogs will again play an important role in the identification of the γ-ray sky.

ID: 154630
Type: article
Authors: de Menezes, Raniere; Peña-Herazo, Harold A.; Marchesini, Ezequiel J.; D'Abrusco, Raffaele; Masetti, Nicola; Nemmen, Rodrigo; Massaro, Francesco; Ricci, Federica; Landoni, Marco; Paggi, Alessandro; Smith, Howard A.
Abstract: Context. Over the last decade more than five thousand γ-ray sources have been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart at lower energies. This has motivated the release of new catalogs of γ-ray counterpart candidates and several follow up campaigns in the last decade.
Aims: Recently, two new catalogs of blazar candidates were released. These are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDEBLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterize these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing their efficiency in selecting true blazars.
Methods: We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. We then analyzed these spectra to verify the nature of each selected candidate and to measure the fraction of the catalogs composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, especially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions.
Results: We found that at least ̃30% of each catalog is made up of confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (≈58%) and normal galaxies in the case of KDEBLLACS (≈38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT fourth Point Source Catalog (4FGL) and to find 25 new BL Lac objects.

ID: 154241
Type: article
Authors: Gustafsson, Annika; Trilling, David E.; Mommert, Michael; McNeill, Andrew; Hora, Joseph L.; Smith, Howard A.; Hellmich, Stephan; Mottola, Stefano; Harris, Alan W.
Abstract: Thermal infrared observations are the most effective way to measure asteroid diameter and albedo for a large number of near-Earth objects (NEOs). Major surveys like NEOWISE, NEOSurvey, ExploreNEOs, and NEOLegacy find a small fraction of high albedo objects that do not have clear analogs in the current meteorite population. About 8% of Spitzer- observed NEOs have nominal albedo solutions greater than 0.5. This may be a result of light-curve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. For a sample of 23 high-albedo NEOs we do not find that their shapes are significantly different from the McNeill et al. NEO shape distribution. We performed a Monte Carlo analysis on 1505 NEOs observed by Spitzer, sampling the visible and thermal fluxes of all targets to determine the likelihood of obtaining a high albedo erroneously. Implementing the McNeill shape distribution for NEOs, we provide an upper limit on the geometric albedo of 0.5 ± 0.1 for the near-Earth population.

ID: 150415
Type: article
Authors: Marchesini, E. J.; Peña-Herazo, H. A.; Álvarez Crespo, N.; Ricci, Federica; Negro, M.; Milisavljevic, D.; Massaro, F.; Masetti, N.; Landoni, M.; Chavushyan, V.; D'Abrusco, Raffaele; Jiménez-Bailón, E.; La Franca, F.; Paggi, A.; Smith, Howard A.; Tosti, G.
Abstract: The third Fermi source catalog lists 3033 γ -ray sources above 4σ significance. More than 30% are classified as either unidentified/unassociated Gamma-ray sources (UGSs), with about 20% classified as Blazar candidates of uncertain types (BCUs). To confirm the blazar-like nature of candidate counterparts of UGSs and BCUs, we started in 2012 an optical spectroscopic follow up campaign. We report here the spectra of 36 targets with observations from the Observatorio Astronómico Nacional San Pedro Mártir, the Southern Astrophysical Research Observatory, the Kitt Peak National Observatory and the Northern Optical Telescope, between 2016 and 2017. We confirm the BL Lac nature of 23 sources, and the flat spectrum radio quasar nature of other 7 ones. We also provide redshift estimates for 19 out of these 30 confirmations, with only one being a lower limit due to spectral features ascribable to intervening systems along the line of sight. As in previous analyses, the largest fraction of now-classified BCUs belong to the class of BL Lac objects, that appear to be the most elusive class of active galactic nuclei. One of the BL Lacs identified in this work, associated with 3FGL J2213.6-4755, lies at a redshift of z>1.529, making it one of the few distant gamma-ray BL Lac objects.

ID: 155155
Type: article
Authors: Peña-Herazo, H. A.; Massaro, F.; Chavushyan, V.; Marchesini, E. J.; Paggi, A.; Landoni, M.; Masetti, N.; Ricci, F.; D'Abrusco, Raffaele; Milisavljevic, D.; Jiménez-Bailón, E.; La Franca, F.; Smith, Howard A.; Tosti, G.
Abstract: Nearly one third of the sources in the Fermi-LAT catalogs lacks a lower energy counterpart, hence being referred as unidentified/unassociated gamma-ray sources (UGSs). In order to firmly classify them, dedicated multifrequency follow-up campaigns are necessary. These will permit to unveil their nature and identify the fraction that could belong to the class of active galaxies known as blazars that is the largest population of extragalactic γ -ray sources. In Fermi-LAT catalogs there are also gamma-ray sources associated with multifrequency blazar-like objects known as Blazars Candidates of Uncertain type (i.e., BCUs) for which follow up spectroscopic campaigns are mandatory to confirm their blazar nature. Thus, in 2013 we started an optical spectroscopic campaign to identify blazar-like objects potential counterparts of UGSs and BCUs. Here we report the spectra of 31 additional targets observed as part of our follow up campaign. Thirteen of them are BCUs for which we acquired spectroscopic observations at Observatorio Astrofísico Guillermo Haro (OAGH) and at Southern Astrophysical Research Observatory (SOAR) telescopes, while the rest has been identified thanks to the archival observations available from the Sloan Digital Sky Survey (SDSS). We confirm the blazar nature of all BCUs: three of them are in blazar of quasar type (BZQs) while the remaining ones can be spectroscopically classified as BL Lac objects (BZBs). Then we also discovered 18 BL Lac objects lying within the positional uncertainty regions of UGSs that could be their potential counterparts.

ID: 150063
Type: article
Authors: Dietrich, Jeremy; Weiner, Aaron S.; Ashby, Matthew L. N.; Hayward, Christopher C.; Martínez-Galarza, Juan Rafael; Ramos Padilla, Andrés F.; Rosenthal, Lee; Smith, Howard A.; Willner, S. P.; Zezas, Andreas
Abstract: Galaxy mergers are key events in galaxy evolution, often causing massive starbursts and fueling active galactic nuclei (AGNs). In these highly dynamic systems, it is not yet precisely known how much starbursts and AGNs, respectively, contribute to the total luminosity, at what interaction stages they occur, and how long they persist. Here we estimate the fraction of the bolometric infrared (IR) luminosity that can be attributed to AGNs by measuring and modeling the full ultraviolet to far-IR spectral energy distributions (SEDs) in up to 33 broad bands for 24 merging galaxies with the Code for Investigating Galaxy Emission. In addition to a sample of 12 confirmed AGNs in late-stage mergers, found in the Infrared Astronomical Satellite Revised Faint Source Catalog, our sample includes a comparison sample of 12 galaxy mergers from the Spitzer Interacting Galaxies Survey, mostly early stage. We also perform SED modeling of merger simulations to validate our methods, and we supplement the SEDs with mid-IR spectra of diagnostic lines obtained with Spitzer's InfraRed Spectrograph. The estimated AGN contributions to the IR luminosities vary from system to system from 0 per cent up to ˜91 per cent but are significantly greater in the later-stage, more luminous mergers, consistent with what is known about galaxy evolution and AGN triggering.

ID: 149376
Type: article
Authors: Hora, Joseph L.; Siraj, Amir; Mommert, Michael; McNeill, Andrew; Trilling, David E.; Gustafsson, Annika; Smith, Howard A.; Fazio, Giovanni G.; Chesley, Steven; Emery, Joshua P.; Harris, Alan; Mueller, Michael
Abstract: We present light curves and derive periods and amplitudes for a subset of 38 near-Earth objects (NEOs) observed at 4.5 μm with the IRAC camera on the the Spitzer Space Telescope, many of them having no previously reported rotation periods. This subset was chosen from about 1800 IRAC NEO observations as having obvious periodicity and significant amplitude. For objects where the period observed did not sample the full rotational period, we derived lower limits to these parameters based on sinusoidal fits. Light curve durations ranged from 42 to 544 minutes, with derived periods from 16 to 270 minutes. We discuss the effects of light curve variations on the thermal modeling used to derive diameters and albedos from Spitzer photometry. We find that both diameters and albedos derived from the light curve maxima and minima agree with our previously published results, even for extreme objects, showing the conservative nature of the thermal model uncertainties. We also evaluate the NEO rotation rates, sizes, and their cohesive strengths.

ID: 146160
Type: article
Authors: Lu, Xing; Zhang, Qizhou; Liu, Hauyu Baobab; Sanhueza, Patricio; Tatematsu, Ken'ichi; Feng, Siyi; Smith, Howard A.; Myers, Philip C.; Sridharan, T. K.; Gu, Qiusheng
Abstract: Filamentary structures are ubiquitous in high-mass star-forming molecular clouds. Their relation with high-mass star formation is still to be understood. Here we report interferometric observations toward eight filamentary high-mass star-forming clouds. A total of 50 dense cores are identified in these clouds, most of which present signatures of high-mass star formation. Five of them are not associated with any star formation indicators and hence are prestellar core candidates. Evolutionary phases of these cores and their line widths, temperatures, {NH}}₃ abundances, and virial parameters are found to be correlated. In a subsample of four morphologically well-defined filaments, we find that their fragmentation cannot be solely explained by thermal or turbulence pressure support. We also investigate distributions of gas temperatures and nonthermal motions along the filaments and find a spatial correlation between nonthermal line widths and star formation activities. We find evidence of gas flows along these filaments and derive an accretion rate along filaments of ∼10^‑4 {M}_ȯ {yr}}^-1. These results suggest a strong relationship between massive filaments and high-mass star formation, through (i) filamentary fragmentation in very early evolutionary phases to form dense cores, (ii) accretion flows along filaments that are important for the growth of dense cores and protostars, and (iii) enhancement of nonthermal motion in the filaments by the feedback or accretion during star formation.

ID: 149173
Type: article
Authors: Martínez-Galarza, J. Rafael; Protopapas, Pavlos; Smith, Howard A.; Morales, Esteban F. E.
Abstract: Despite significant evidence suggesting that intermediate- and high-mass stars form in clustered environments, how stars form when the available resources are shared is still not well understood. A related question is whether the initial mass function (IMF) is in fact universal across galactic environments, or whether it is an average of IMFs that differ, for example, in massive versus low-mass molecular clouds. One of the long-standing problems in resolving these questions and in the study of young clusters is observational: how to accurately combine multiwavelength data sets obtained using telescopes with different spatial resolutions. The resulting confusion hinders our ability to fully characterize clustered star formation. Here we present a new method that uses Bayesian inference to fit the blended spectral energy distributions and images of individual young stellar objects (YSOs) in confused clusters. We apply this method to the infrared photometry of a sample comprising 70 Spitzer-selected, low-mass (M _{cl ⊙}) young clusters in the galactic plane, and we use the derived physical parameters to investigate how the distribution of YSO masses within each cluster relates to the total mass of the cluster. We find that for low-mass clusters this distribution is indistinguishable from a randomly sampled Kroupa IMF for this range of cluster masses. Therefore, any effects of self-regulated star formation that affect the IMF sampling are likely to play a role only at larger cluster masses. Our results are also compatible with smoothed particle hydrodynamics models that predict a dynamical termination of the accretion in protostars, with massive stars undergoing this stopping at later times in their evolution.

ID: 150221
Type: article
Authors: Trilling, David E.; Mommert, Michael; Hora, Joseph L.; Farnocchia, Davide; Chodas, Paul; Giorgini, Jon; Smith, Howard A.; Carey, Sean; Lisse, Carey M.; Werner, Michael; McNeill, Andrew; Chesley, Steven R.; Emery, Joshua P.; Fazio, Giovanni G.; Fernandez, Yanga R.; Harris, Alan; Marengo, Massimo; Mueller, Michael; Roegge, Alissa; Smith, Nathan; Weaver, H. A.; Meech, Karen; Micheli, Marco
Abstract: 1I/‘Oumuamua is the first confirmed interstellar body in our solar system. Here we report on observations of ‘Oumuamua made with the Spitzer Space Telescope on 2017 November 21–22 (UT). We integrated for 30.2 hr at 4.5 μm (IRAC channel 2). We did not detect the object and place an upper limit on the flux of 0.3 μJy (3σ). This implies an effective spherical diameter less than [98, 140, 440] m and albedo greater than [0.2, 0.1, 0.01] under the assumption of low, middle, or high thermal beaming parameter η, respectively. With an aspect ratio for ‘Oumuamua of 6:1, these results correspond to dimensions of [240:40, 341:57, 1080:180] m, respectively. We place upper limits on the amount of dust, CO, and CO₂ coming from this object that are lower than previous results; we are unable to constrain the production of other gas species. Both our size and outgassing limits are important because ‘Oumuamua’s trajectory shows non-gravitational accelerations that are sensitive to size and mass and presumably caused by gas emission. We suggest that ‘Oumuamua may have experienced low-level post-perihelion volatile emission that produced a fresh, bright, icy mantle. This model is consistent with the expected η value and implied high-albedo value for this solution, but, given our strict limits on CO and CO₂, requires another gas species—probably H₂O—to explain the observed non-gravitational acceleration. Our results extend the mystery of ‘Oumuamua’s origin and evolution.

ID: 142327
Type: article
Authors: Massaro, Francesco; Marchesini, E. J.; D'Abrusco, R.; Masetti, N.; Andruchow, I.; Smith, Howard A.
Abstract: The existence of "radio-weak BL Lac objects" (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]–[4.6]–[12] μm color–color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.

ID: 139166
Type: article
Authors: Álvarez Crespo, N.; Masetti, N.; Ricci, F.; Landoni, M.; Patiño-Álvarez, V.; Massaro, Francesco; D'Abrusco, R.; Paggi, A.; Chavushyan, V.; Jiménez-Bailón, E.; Torrealba, J.; Latronico, L.; La Franca, F.; Smith, Howard A.; Tosti, G.
Abstract: The extragalactic γ-ray sky is dominated by emission from blazars, a peculiar class of active galactic nuclei. Many of the γ-ray sources included in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs) because there are no optical spectra available in the literature to confirm their nature. In 2013, we started a spectroscopic campaign to look for the optical counterparts of the BCUs and of the unidentified γ-ray sources to confirm their blazar nature. Whenever possible we also determine their redshifts. Here, we present the results of the observations carried out in the northern hemisphere in 2013 and 2014 at the Telescopio Nazionale Galileo, Kitt Peak National Observatory, and Observatorio Astronómico Nacional in San Pedro Mártir. In this paper, we describe the optical spectra of 25 sources. We confirmed that all of the 15 BCUs observed in our campaign and included in our sample are blazars and we estimated the redshifts for three of them. In addition, we present the spectra for three sources classified as BL Lacs in the literature but with no optical spectra available to date. We found that one of them is a quasar (QSO) at a redshift of z = 0.208 and the other two are BL Lacs. Moreover, we also present seven new spectra for known blazars listed in the Roma-BZCAT that have an uncertain redshift or are classified as BL Lac candidates. We found that one of them, 5BZB J0724+2621, is a "changing look" blazar. According to the spectrum available in the literature, it was classified as a BL Lac, but in our observation we clearly detected a broad emission line that led us to classify this source as a QSO at z = 1.17.

ID: 140790
Type: article
Authors: Álvarez Crespo, N.; Massaro, Francesco; D'Abrusco, Raffaele; Landoni, M.; Masetti, N.; Chavushyan, V.; Jiménez-Bailón, E.; La Franca, F.; Milisavljevic, D.; Paggi, A.; Patiño-Álvarez, V.; Ricci, F.; Smith, Howard A.
Abstract: Despite the fact that blazars constitute the rarest class among active galactic nuclei (AGNs) they are the largest known population of associated γ-ray sources. Many of the γ-ray objects listed in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs), either because they show multifrequency behavior similar to blazars but lacking optical spectra in the literature, or because the quality of such spectra is too low to confirm their nature. Here we select, out of 585 BCUs in the 3FGL, 42 BCUs which we identify as probable blazars by their WISE infrared colors and which also have optical spectra that are available in the Sloan Digital Sky Survey (SDSS) and/or Six-Degree Field Galaxy Survey Database (6dFGS). We confirm the blazar nature of all of the sources. We furthermore conclude that 28 of them are BL Lacs, 8 are radio-loud quasars with flat radio spectrum and 6 are BL Lac whose emission is dominated by their host galaxy.