Publication Search Results

ID: 158022
Type: article
Authors: Aouad, Charles J.; James, Philip A.; Chilingarian, Igor V.
Abstract: Star formation is one of the key factors that shapes galaxies. This process is relatively well understood from both simulations and observations on a small 'local' scale of individual giant molecular clouds (GMCs) and also on a 'global' galaxy-wide scale (e.g. the Kennicutt-Schmidt law). However, there is still no understanding on how to connect global to local star formation scales and whether this connection is at all possible. Here, we analyse spatially resolved kinematics and the star formation rate (SFR) density Σ_SFR for a combined sample of 17 nearby spiral galaxies obtained using our own optical observations in Hα for nine galaxies and neutral hydrogen radio observations combined with a multiwavelength spectral energy distribution analysis for eight galaxies from the THINGS project. We show that the azimuthally averaged normalized SFR density in spiral galaxies on a scale of a few hundred parsecs is proportional to the kinetic energy of GMC collisions due to differential rotation of the galactic disc. This energy is calculated from the rotation curve using the two Oort parameters A and B as log (Σ_SFR/SFR_tot)∝log [2A² + 5B²]. The total kinetic energy of collision is defined by the shear velocity that is proportional to A and the spin energy of a cloud proportional to the vorticity B. Hence, shear does not act as a stabilizing factor for the cloud collapse thus reducing star formation but rather increases it by boosting the kinetic energy of collisions.

ID: 156976
Type: article
Authors: Coppejans, D. L.; Margutti, R.; Terreran, G.; Nayana, A. J.; Coughlin, E. R.; Laskar, T.; Alexander, K. D.; Bietenholz, M.; Caprioli, D.; Chandra, P.; Drout, M. R.; Frederiks, D.; Frohmaier, C.; Hurley, K. H.; Kochanek, C. S.; MacLeod, Morgan; Meisner, A.; Nugent, P. E.; Ridnaia, A.; Sand, D. J.; Svinkin, D.; Ward, C.; Yang, S.; Baldeschi, A.; Chilingarian, Igor V.; Dong, Y.; Esquivia, C.; Fong, W.; Guidorzi, C.; Lundqvist, P.; Milisavljevic, D.; Paterson, K.; Reichart, D. E.; Shappee, B.; Stroh, M. C.; Valenti, S.; Zauderer, B. A.; Zhang, B.
Abstract: We present X-ray and radio observations of the Fast Blue Optical Transient CRTS-CSS161010 J045834-081803 (CSS161010 hereafter) at t = 69-531 days. CSS161010 shows luminous X-ray (L_X ∼ 5 × 10³⁹ erg s^-1) and radio (L_ν ∼ 10²⁹ erg s^-1 Hz^-1) emission. The radio emission peaked at ∼100 days post-transient explosion and rapidly decayed. We interpret these observations in the context of synchrotron emission from an expanding blast wave. CSS161010 launched a mildly relativistic outflow with velocity Γβc ≥ 0.55c at ∼100 days. This is faster than the non-relativistic AT 2018cow (Γβc ∼ 0.1c) and closer to ZTF18abvkwla (Γβc ≥ 0.3c at 63 days). The inferred initial kinetic energy of CSS161010 (E_k ≳ 10⁵¹ erg) is comparable to that of long gamma-ray bursts, but the ejecta mass that is coupled to the mildly relativistic outflow is significantly larger ( $\sim 0.01\mbox{--}0.1\,{M}_{\odot }$ ). This is consistent with the lack of observed γ-rays. The luminous X-rays were produced by a different emission component to the synchrotron radio emission. CSS161010 is located at ∼150 Mpc in a dwarf galaxy with stellar mass M_* ∼ 10⁷ M_☉ and specific star formation rate sSFR ∼ 0.3 Gyr^-1. This mass is among the lowest inferred for host galaxies of explosive transients from massive stars. Our observations of CSS161010 are consistent with an engine-driven aspherical explosion from a rare evolutionary path of a H-rich stellar progenitor, but we cannot rule out a stellar tidal disruption event on a centrally located intermediate-mass black hole. Regardless of the physical mechanism, CSS161010 establishes the existence of a new class of rare (rate < 0.4% of the local core-collapse supernova rate) H-rich transients that can launch mildly relativistic outflows.

ID: 158023
Type: article
Authors: Kasparova, Anastasia V.; Katkov, Ivan Yu; Chilingarian, Igor V.
Abstract: Galactic discs are known to have a complex multilayer structure. An in-depth study of the stellar population properties of the thin and thick components can elucidate the formation and evolution of disc galaxies. Even though thick discs are ubiquitous, their origin is still debated. Here we probe the thick disc formation scenarios by investigating NGC 7572, an enormous edge-on galaxy having R₂₅ ≈ 25 kpc and V_rot ≈ 370 km s^-1, which substantially exceeds the Milky Way size and mass. We analysed DECaLS archival imaging and found that the disc of NGC 7572 contains two flaring stellar discs (a thin and a thick disc) with similar radial scales. We collected deep long-slit spectroscopic data using the 6 m Russian BTA telescope and analysed them with a novel technique. We first reconstructed a non-parametric stellar line-of-sight velocity distribution along the radius of the galaxy and then fitted it with two kinematic components accounting for the orbital distribution of stars in thin and thick discs. The old thick disc turned out to be 2.7 times as massive as the intermediate-age thin component, 1.6 × 10¹¹ M_☉ versus 5.9 × 10¹⁰ M_☉, which is very unusual. The different duration of the formation epochs evidenced by the [Mg/Fe] values of +0.3 and +0.15 dex for the thick and thin discs respectively, their kinematics, and the mass ratio suggest that in NGC 7572 we observe a rapidly formed very massive thick disc and an underdeveloped thin disc, whose growth ended prematurely due to the exhaustion of the cold gas likely because of environmental effects.

ID: 158021
Type: article
Authors: Maschmann, Daniel; Melchior, Anne-Laure; Mamon, Gary A.; Chilingarian, Igor V.; Katkov, Ivan Yu
Abstract: Double-peak narrow emission line galaxies have been studied extensively in the past years, in the hope of discovering late stages of mergers. It is difficult to disentangle this phenomenon from disc rotations and gas outflows with the sole spectroscopic measurement of the central 3″. We aim to properly detect such galaxies and distinguish the underlying mechanisms with a detailed analysis of the host-galaxy properties and their kinematics. Relying on the Reference Catalogue of Spectral Energy Distribution, we developed an automated selection procedure and found 5663 double-peak emission line galaxies at z < 0.34 corresponding to 0.8% of the parent database. To characterise these galaxies, we built a single-peak no-bias control sample (NBCS) with the same redshift and stellar mass distributions as the double-peak sample (DPS). These two samples are indeed very similar in terms of absolute magnitude, [OIII] luminosity, colour-colour diagrams, age and specific star formation rate, metallicity, and environment. We find an important excess of S0 galaxies in the DPS, not observed in the NBCS, which cannot be accounted for by the environment, as most of these galaxies are isolated or in poor groups. Similarly, we find a relative deficit of pure discs in the DPS late-type galaxies, which are preferentially of Sa type. In parallel, we observe a systematic central excess of star formation and extinction for double peak (DP) galaxies. Finally, there are noticeable differences in the kinematics: The gas velocity dispersion is correlated with the galaxy inclination in the NBCS, whereas this relation does not hold for the DPS. Furthermore, the DP galaxies show larger stellar velocity dispersions and they deviate from the Tully-Fisher relation for both late-type and S0 galaxies. These discrepancies can be reconciled if one considers the two peaks as two different components. Considering the morphological biases in favour of bulge-dominated galaxies and the star formation central enhancement, we suggest a scenario of multiple, sequential minor mergers driving the increase of the bulge size, leading to larger fractions of S0 galaxies and a deficit of pure disc galaxies.

ID: 156980
Type: article
Authors: Raymond, John C.; Chilingarian, Igor V.; Blair, William P.; Sankrit, Ravi; Slavin, Jonathan D.; Burkhart, Blakesley
Abstract: We have obtained a contiguous set of long-slit spectra of a shock wave in the Cygnus Loop to investigate its structure, which is far from the morphology predicted by 1D models. Proper motions from Hubble Space Telescope images combined with the known distance to the Cygnus Loop provide an accurate shock speed. Earlier analyses of shock spectra estimated the shock speed, postshock density, temperature, and elemental abundances. In this paper we determine several more shock parameters: a more accurate shock speed, ram pressure, density, compression ratio, dust destruction efficiency, magnetic field strength, and vorticity in the cooling region. From the derived shock properties we estimate the emissivities of synchrotron emission in the radio and pion decay emission in the gamma-rays. Both are consistent with the observations if we assume simple adiabatic compression of ambient cosmic-rays as in the van der Laan mechanism. We also find that, although the morphology is far from that predicted by 1D models and the line ratios vary dramatically from point to point, the average spectrum is matched reasonably well by 1D shock models with the shock speed derived from the measured proper motion. A subsequent paper will analyze the development of turbulence in the cooling zone behind the shock.

ID: 158750
Type: article
Authors: Raymond, John C.; Slavin, Jonathan D.; Blair, William P.; Chilingarian, Igor V.; Burkhart, Blakesley; Sankrit, Ravi
Abstract: Radiative shock waves in the Cygnus Loop and other supernova remnants show different morphologies in [O III] and Ha emission. We use HST spectra and narrowband images to study the development of turbulence in the cooling region behind a shock on the west limb of the Cygnus Loop. We refine our earlier estimates of shock parameters that were based upon ground-based spectra, including ram pressure, vorticity, and magnetic field strength. We apply several techniques, including Fourier power spectra and the Rolling Hough Transform, to quantify the shape of the rippled shock front as viewed in different emission lines. We assess the relative importance of thermal instabilities, the thin shell instability, upstream density variations, and upstream magnetic field variations in producing the observed structure.

ID: 154712
Type: article
Authors: Chilingarian, Igor V.; Afanasiev, Anton V.; Grishin, Kirill A.; Fabricant, Daniel; Moran, Sean
Abstract: Ultra-diffuse galaxies (UDGs) are spatially extended, low surface brightness stellar systems with regular elliptical-like morphology found in a wide range of environments. Studies of the internal dynamics and dark matter content of UDGs that would elucidate their formation and evolution have been hampered by their low surface brightnesses. Here, we present spatially resolved velocity profiles, stellar velocity dispersions, ages, and metallicities for nine UDGs in the Coma cluster. We use intermediate-resolution spectra obtained with Binospec, the MMT's new high-throughput optical spectrograph. We derive dark matter fractions between 50% and 90% within the half-light radius using Jeans dynamical models. Three galaxies exhibit major axis rotation, two others have highly anisotropic stellar orbits, and one shows signs of triaxiality. In the Faber-Jackson and mass-metallicity relations, the nine UDGs fill the gap between cluster dwarf elliptical (dE) and fainter dwarf spheroidal galaxies. Overall, the observed properties of all nine UDGs can be explained by a combination of internal processes (supernovae feedback) and environmental effects (ram pressure stripping, interaction with neighbors). These observations suggest that UDGs and dEs are members of the same galaxy population. All galaxy spectra presented in this work and their best-fitting stellar population templates are available at the following permanent address: https://doi.org/10.5281/zenodo.3387745.

ID: 154168
Type: article
Authors: Fabricant, Daniel; Fata, Robert; Epps, Harland; Gauron, Thomas; Mueller, Mark; Zajac, Joseph; Amato, Stephen; Barberis, Jack; Bergner, Henry; Brennan, Patricia; Brown, Warren; Chilingarian, Igor; Geary, John; Kradinov, Vladimir; McLeod, Brian; Smith, Matthew C.; Woods, Deborah
Abstract: Binospec is a high-throughput, 370 to 1000 nm, imaging spectrograph that addresses two adjacent 8′ by 15′ fields of view. Binospec was commissioned in late 2017 at the f/5 focus of the 6.5 m MMT and is now available to all MMT observers. Aperture masks cut from stainless steel with a laser cutter are used to define the entrance apertures that range from 15′ long slits to hundreds of 2″ slitlets. System throughputs, including the MMT's mirrors and the f/5 wide-field corrector peak at ̃30%. Three reflection gratings, duplicated for the two beams, provide resolutions (λ/∆λ) between 1300 and >5000 with a 1″ wide slit. Two through-the-mask guiders are used for target acquisition, mask alignment, guiding, and precision offsets. A full-time Shack-Hartmann wavefront sensor allows continuous adjustment of primary mirror support forces, telescope collimation and focus. Active flexure control maintains spectrograph alignment and focus under varying gravity and thermal conditions.

ID: 154169
Type: article
Authors: Kansky, Jan; Chilingarian, Igor; Fabricant, Daniel; Matthews, Anne; Moran, Sean; Paegert, Martin; Duane Gibson, J.; Porter, Dallan; Roll, John
Abstract: Binospec is a high-throughput, 370 to 1000 nm, imaging spectrograph that addresses two adjacent 8′ by 15′ fields of view. Binospec was commissioned in late 2017 at the f/5 focus of the 6.5 m MMT and is now available to all MMT observers. Here we describe the Binospec software used for observation planning, instrument control, and data reduction. The software and control systems incorporate a high level of automation to minimize observer workload. Instrument configuration and observation sequencing is implemented using a database-driven approach to maximize observatory efficiency. A web-based interface allows users to define observations, monitor status, and retrieve data products.

ID: 150513
Type: article
Authors: Margutti, R.; Metzger, B. D.; Chornock, R.; Vurm, I.; Roth, N.; Grefenstette, B. W.; Savchenko, V.; Cartier, R.; Steiner, J. F.; Terreran, G.; Margalit, B.; Migliori, G.; Milisavljevic, D.; Alexander, K. D.; Bietenholz, M.; Blanchard, Peter K.; Bozzo, E.; Brethauer, D.; Chilingarian, Igor V.; Coppejans, D. L.; Ducci, L.; Ferrigno, C.; Fong, W.; Götz, D.; Guidorzi, C.; Hajela, A.; Hurley, K.; Kuulkers, E.; Laurent, P.; Mereghetti, S.; Nicholl, M.; Patnaude, Daniel; Ubertini, P.; Banovetz, J.; Bartel, N.; Berger, Edo; Coughlin, E. R.; Eftekhari, T.; Frederiks, D. D.; Kozlova, A. V.; Laskar, T.; Svinkin, D. S.; Drout, M. R.; MacFadyen, A.; Paterson, K.
Abstract: We present the first extensive radio to γ-ray observations of a fast-rising blue optical transient, AT 2018cow, over its first ∼100 days. AT 2018cow rose over a few days to a peak luminosity L _pk ∼ 4 × 10⁴⁴ erg s^‑1, exceeding that of superluminous supernovae (SNe), before declining as L ∝ t ^‑2. Initial spectra at δt ≲ 15 days were mostly featureless and indicated large expansion velocities v ∼ 0.1c and temperatures reaching T ∼ 3 × 10⁴ K. Later spectra revealed a persistent optically thick photosphere and the emergence of H and He emission features with v ∼ 4000 km s^‑1 with no evidence for ejecta cooling. Our broadband monitoring revealed a hard X-ray spectral component at E ≥ 10 keV, in addition to luminous and highly variable soft X-rays, with properties unprecedented among astronomical transients. An abrupt change in the X-ray decay rate and variability appears to accompany the change in optical spectral properties. AT 2018cow showed bright radio emission consistent with the interaction of a blast wave with v _sh ∼ 0.1c with a dense environment (\dot{M}∼ {10}^-3-{10}^-4 {M}_ȯ {yr}}^-1 for v _w = 1000 km s^‑1). While these properties exclude ⁵⁶Ni-powered transients, our multiwavelength analysis instead indicates that AT 2018cow harbored a “central engine,” either a compact object (magnetar or black hole) or an embedded internal shock produced by interaction with a compact, dense circumstellar medium. The engine released ∼10⁵⁰–10^51.5 erg over ∼10³–10⁵ s and resides within low-mass fast-moving material with equatorial–polar density asymmetry (M _ej,fast ≲ 0.3 M _⊙). Successful SNe from low-mass H-rich stars (like electron-capture SNe) or failed explosions from blue supergiants satisfy these constraints. Intermediate-mass black holes are disfavored by the large environmental density probed by the radio observations.

ID: 154598
Type: article
Authors: Saburova, Anna S.; Chilingarian, Igor V.; Kasparova, Anastasia V.; Katkov, Ivan Yu; Fabricant, Daniel G.; Uklein, Roman I.
Abstract: The dominant physical processes responsible for the formation and longevity of giant gaseous and stellar discs in galaxies remain controversial. Although they are rare (less than 10 confirmed as of now), giant low-surface brightness (gLSB) discy galaxies provide interesting insights given their extreme nature. We describe observations of UGC 1378 including deep spectroscopy with the Russian 6-m telescope and multiband imaging with Binospec at the MMT. Galaxy UGC 1378 has both high surface brightness and an extended low surface brightness discs. Our stellar velocity dispersion data for the high surface brightness, Milky Way sized, disc appears inconsistent with a recent major merger, a widely discussed formation scenario for the very extended low surface brightness disc. We estimate the star formation rates (SFRs) from archival Wide-Field Infrared Survey Explorer data. The SFR surface density in the LSB disc is low relative to its gas density, consistent with recent gas accretion. We argue that the unusually large size of UGC 1378's disc may be the product of a rich gas reservoir (e.g. a cosmic filament) and an isolated environment that has preserved the giant disc.

ID: 147888
Type: article
Authors: Afanasiev, Anton V.; Chilingarian, Igor V.; Mieske, Steffen; Voggel, Karina T.; Picotti, Arianna; Hilker, Michael; Seth, Anil; Neumayer, Nadine; Frank, Matthias; Romanowsky, Aaron J.; Hau, George; Baumgardt, Holger; Ahn, Christopher; Strader, Jay; den Brok, Mark; McDermid, Richard; Spitler, Lee; Brodie, Jean; Walsh, Jonelle L.
Abstract: The origin of ultracompact dwarfs (UCDs), a class of compact stellar systems discovered two decades ago, still remains a matter of debate. Recent discoveries of central supermassive black holes in UCDs likely inherited from their massive progenitor galaxies provide support for the tidal stripping hypothesis. At the same time, on statistical grounds, some massive UCDs might be representatives of the high luminosity tail of the globular cluster luminosity function. Here we present a detection of a 3.3^{+1.4}_{-1.2}× 10^6 M_{&sun;} black hole (1sigma uncertainty) in the centre of the UCD3 galaxy in the Fornax cluster, which corresponds to 4 per cent of its stellar mass. We performed isotropic Jeans dynamical modelling of UCD3 using internal kinematics derived from adaptive optics-assisted observations with the SINFONI spectrograph and seeing limited data collected with the FLAMES spectrograph at the ESO VLT. We rule out the zero black hole mass at the 3sigma confidence level when adopting a mass-to-light ratio inferred from stellar populations. This is the fourth supermassive black hole found in a UCD and the first one in the Fornax cluster. Similarly to other known UCDs that harbour black holes, UCD3 hosts metal rich stars enhanced in alpha-elements that support the tidal stripping of a massive progenitor as its likely formation scenario. We estimate that up to 80 per cent of luminous UCDs in galaxy clusters host central black holes. This fraction should be lower for UCDs in groups, because their progenitors are more likely to be dwarf galaxies, which do not usually host black holes massive enough to be detected.

ID: 149381
Type: article
Authors: Raymond, John C.; Koo, B. -C; Lee, Y. -H; Milisavljevic, D.; Fesen, R. A.; Chilingarian, I.
Abstract: The supernova remnant Cassiopeia A (Cas A) is one of the few remnants in which it is possible to observe unshocked ejecta. A deep 1.64 μm image of Cas A shows a patch of diffuse emission from unshocked ejecta, as well as brighter emission from fast-moving knots and quasi-stationary flocculi. Emission at 1.64 μm is usually interpreted as [Fe II] emission, and spectra of the bright knots confirm this by showing the expected emission in other [Fe II] lines. We performed near-infrared spectroscopy on the diffuse emission region and found that the unshocked ejecta emission does not show those lines, but rather shows the [Si I] 1.607 μm line. This means that the 1.64 μm line from the unshocked ejecta may be the [Si I] 1.645 line from the same upper level, rather than [Fe II]. We find that the [Si I] line is formed by recombination, and we use the [Si I] to [Si II] ratio to infer a temperature of about 100 K, which is close to the value assumed for an analysis of low-frequency radio absorption and that can be inferred from emission by cool dust. Our results constrain estimates of Cas A's total mass of unshocked ejecta that are extremely sensitive to temperature assumptions, but they do not resolve the ambiguity due to clumping.

ID: 150216
Type: article
Authors: Saburova, Anna S.; Chilingarian, Igor V.; Katkov, Ivan Yu; Egorov, Oleg V.; Kasparova, Anastasia V.; Khoperskov, Sergey A.; Uklein, Roman I.; Vozyakova, Olga V.
Abstract: The formation scenario for giant low surface brightness (gLSB) galaxies with discs as large as 100 kpc still remains unclear. These stellar systems are rare and very hard to observe, therefore a detailed insight on every additional object helps to understand their nature. Here we present a detailed observational study of the gLSB UGC 1922 performed using deep optical imaging and spectroscopic observations combined with archival ultraviolet data. We derived spatially resolved properties of stellar and ionized gas kinematics and characteristics of stellar populations and interstellar medium. We reveal the presence of a kinematically decoupled central component, which counter rotates with respect to the main disc of UGC 1922. The radial metallicity gradient of the ionized gas is in agreement with that found for moderate-size LSB galaxies. At the same time, a slowly rotating and dynamically hot central region of the galaxy hosts a large number of old metal-rich stars, which creates an appearance of a giant elliptical galaxy, that grew an enormous star forming disc. We reproduce most of the observed features of UGC 1922 in N-body/hydrodynamical simulations of an in-plane merger of giant Sa and Sd galaxies. We also discuss alternative formation scenarios of this unusual system.

ID: 143278
Type: article
Authors: Ahn, Christopher P.; Seth, Anil C.; den Brok, Mark; Strader, Jay; Baumgardt, Holger; van den Bosch, Remco; Chilingarian, Igor; Frank, Matthias; Hilker, Michael; McDermid, Richard; Mieske, Steffen; Romanowsky, Aaron J.; Spitler, Lee; Brodie, Jean; Neumayer, Nadine; Walsh, Jonelle L.
Abstract: We present the detection of supermassive black holes (BHs) in two Virgo ultracompact dwarf galaxies (UCDs), VUCD3 and M59cO. We use adaptive optics assisted data from the Gemini/NIFS instrument to derive radial velocity dispersion profiles for both objects. Mass models for the two UCDs are created using multi-band Hubble Space Telescope imaging, including the modeling of mild color gradients seen in both objects. We then find a best-fit stellar mass-to-light ratio (M/L) and BH mass by combining the kinematic data and the deprojected stellar mass profile using Jeans Anisotropic Models. Assuming axisymmetric isotropic Jeans models, we detect BHs in both objects with masses of {4.4}_-3.0^+2.5× {10}⁶ M _? in VUCD3 and {5.8}_-2.8^+2.5× {10}⁶ M _? in M59cO (3? uncertainties). The BH mass is degenerate with the anisotropy parameter, {? }_z; for the data to be consistent with no BH requires {? }_z=0.4 and {? }_z=0.6 for VUCD3 and M59cO, respectively. Comparing these values with nuclear star clusters shows that, while it is possible that these UCDs are highly radially anisotropic, it seems unlikely. These detections constitute the second and third UCDs known to host supermassive BHs. They both have a high fraction of their total mass in their BH; ~13% for VUCD3 and ~18% for M59cO. They also have low best-fit stellar M/Ls, supporting the proposed scenario that most massive UCDs host high-mass fraction BHs. The properties of the BHs and UCDs are consistent with both objects being the tidally stripped remnants of ~ {10}⁹ {{{M}}}_o galaxies.

ID: 143326
Type: article
Authors: Graham, Alister W.; Janz, Joachim; Penny, Samantha J.; Chilingarian, Igor V.; Ciambur, Bogdan C.; Forbes, Duncan A.; Davies, Roger L.
Abstract: Selected from a sample of nine, isolated, dwarf early-type galaxies (ETGs) with the same range of kinematic properties as dwarf ETGs in clusters, we use LEDA 2108986 (CG 611) to address the nature versus nurture debate regarding the formation of dwarf ETGs. The presence of faint disk structures and rotation within some cluster dwarf ETGs has often been heralded as evidence that they were once late-type spiral or dwarf irregular galaxies prior to experiencing a cluster-induced transformation into an ETG. However, CG 611 also contains significant stellar rotation (?20 km s^-1) over its inner half-light radius ({R}_{{e},{maj}}=0.71 kpc), and its stellar structure and kinematics resemble those of cluster ETGs. In addition to hosting a faint young nuclear spiral within a possible intermediate-scale stellar disk, CG 611 has accreted an intermediate-scale, counter-rotating gas disk. It is therefore apparent that dwarf ETGs can be built by accretion events, as opposed to disk-stripping scenarios. We go on to discuss how both dwarf and ordinary ETGs with intermediate-scale disks, whether under (de)construction or not, are not fully represented by the kinematic scaling {S}_0.5=\sqrt{0.5 {V}_{rot}²+{? }²}, and we also introduce a modified spin-ellipticity diagram ? (R)-? (R) with the potential to track galaxies with such disks.

ID: 144724
Type: article
Authors: Milisavljevic, Dan; Patnaude, Daniel J.; Raymond, John C.; Drout, Maria R.; Margutti, Raffaella; Kamble, Atish; Chornock, Ryan; Guillochon, James; Sanders, Nathan E.; Parrent, Jerod T.; Lovisari, Lorenzo; Chilingarian, Igor V.; Challis, Peter; Kirshner, Robert P.; Penny, Matthew T.; Itagaki, Koichi; Eldridge, J. J.; Moriya, Takashi J.
Abstract: The progenitor systems of the class of "Ca-rich transients" is a key open issue in time domain astrophysics. These intriguing objects exhibit unusually strong calcium line emissions months after explosion, fall within an intermediate luminosity range, are often found at large projected distances from their host galaxies, and may play a vital role in enriching galaxies and the intergalactic medium. Here we present multiwavelength observations of iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that bridge those observed in Ca-rich transients and SNe Ib/c. iPTF15eqv has among the highest [Ca II]/[O I] emission line ratios observed to date, yet is more luminous and decays more slowly than other Ca-rich transients. Optical and near-infrared photometry and spectroscopy reveal signatures consistent with the supernova explosion of a ? 10 {M}_? star that was stripped of its H-rich envelope via binary interaction. Distinct chemical abundances and ejecta kinematics suggest that the core collapse occurred through electron-capture processes. Deep limits on possible radio emission made with the Jansky Very Large Array imply a clean environment (n ? 0.1 cm^-3) within a radius of ~ {10}¹⁷ cm. Chandra X-ray Observatory observations rule out alternative scenarios involving the tidal disruption of a white dwarf (WD) by a black hole, for masses >100 M _?. Our results challenge the notion that spectroscopically classified Ca-rich transients only originate from WD progenitor systems, complicate the view that they are all associated with large ejection velocities, and indicate that their chemical abundances may vary widely between events.

ID: 143272
Type: article
Authors: Zolotukhin, Ivan Yu; Bachetti, Matteo; Sartore, Nicola; Chilingarian, Igor V.; Webb, Natalie A.
Abstract: Neutron stars are thought to be born rapidly rotating and then exhibit a phase of rotation-powered pulsations as they slow down to 1-10 s periods. The significant population of millisecond pulsars observed in our Galaxy is explained by the recycling concept: during an epoch of accretion from a donor star in a binary system, the neutron star is spun up to millisecond periods. However, only a few pulsars are observed during this recycling process, with relatively high rotational frequencies. Here we report the detection of an X-ray pulsar with {P}_{spin}=1.20 {{s}} in the globular cluster B091D in the Andromeda galaxy, the slowest pulsar ever found in a globular cluster. This bright (up to 30% of the Eddington luminosity) spinning-up pulsar, persistent over the 12 years of observations, must have started accreting less than 1 Myr ago and has not yet had time to accelerate to hundreds of Hertz. The neutron star in this unique wide binary with an orbital period {P}_{orb}=30.5 {hr} in a 12 Gyr old, metal-rich star cluster accretes from a low-mass, slightly evolved post-main-sequence companion. We argue that we are witnessing a binary formed at a relatively recent epoch by getting a ~0.8 {M}_o star in a dynamical interaction-a viable scenario in a massive, dense globular cluster like B091D with high global and specific stellar encounter rates. This intensively accreting non-recycled X-ray pulsar therefore provides a long-sought missing piece in the standard pulsar recycling picture.

ID: 139977
Type: article
Authors: Kasparova, Anastasia V.; Katkov, Ivan Yu; Chilingarian, Igor V.; Silchenko, Olga K.; Moiseev, Alexey V.; Borisov, Svyatoslav B.
Abstract: Although thick stellar discs are detected in nearly all edge-on disc galaxies, their formation scenarios still remain a matter of debate. Due to observational difficulties, there is a lack of information about their stellar populations. Using the Russian 6-m telescope BTA we collected deep spectra of thick discs in three edge-on S0-a disc galaxies located in different environments: NGC 4111 in a dense group, NGC 4710 in the Virgo cluster, and NGC 5422 in a sparse group. We see intermediate age (4-5 Gyr) metal rich ([Fe/H] ˜- 0.2…0.0 dex) stellar populations in NGC 4111 and NGC 4710. On the other hand, NGC 5422 does not harbour young stars, its disc is thick and old (10 Gyr), without evidence for a second component, and its a-element abundance suggests a 1.5-2 Gyr long formation epoch implying its formation at high redshift. Our results suggest the diversity of thick disc formation scenarios.

ID: 140766
Type: article
Authors: Katkov, Ivan Yu; Sil'chenko, Olga K.; Chilingarian, Igor V.; Uklein, Roman I.; Egorov, Oleg V.
Abstract: The counter-rotation phenomenon in disc galaxies directly indicates a complex galaxy assembly history which is crucial for our understanding of galaxy physics. Here, we present the complex data analysis for a lenticular galaxy NGC 448, which has been recently suspected to host a counter-rotating stellar component. We collected deep long-slit spectroscopic observations using the Russian 6-m telescope and performed the photometric decomposition of Sloan Digital Sky Survey archival images. We exploited (i) a non-parametric approach in order to recover stellar line-of-sight velocity distributions and (ii) a parametric spectral decomposition technique in order to disentangle stellar population properties of both main and counter-rotating stellar discs. Our spectral decomposition stays in perfect agreement with the photometric analysis. The counter-rotating component contributes ˜30 per cent to the total galaxy light. We estimated its stellar mass to be 9.0^{+2.7}_{-1.8}× 10⁹ M_{?}. The radial scalelength of counter-rotating disc is ˜3 times smaller than that of the main disc. Both discs harbour old stars but the counter-rotating components reveal a detectable negative age gradient that might suggest an extended inside-out formation during 3…4 Gyr. The counter-rotating disc hosts more metal-rich stars and possesses a shallower metallicity gradient with respect to the main disc. Our findings rule out cosmological filaments as a source of external accretion which is considered as a potential mechanism of the counter-rotating component formation in NGC 448, and favour the satellite merger event with the consequent slow gas accretion.