Low Stellar Mass Research Articles

Mufasa: Time-scales for H i consumption and SFR depletion of satellite galaxies in groups

We investigate the connection between the HI~content, SFR and environment of galaxies using a hydrodynamic simulation that incorporates scaling relations for galactic wind and a heuristic halo mass-based quenching prescription. We run two zoom-in simulations of galaxy groups with $M_{halo}>10^{13}M_\odot$ at z=0, selected to have quiet merger histories. We track galaxies as they become satellites, and compute the delay time $\tau_{d}$ during which the satellites are similar to central galaxies at a given stellar mass, and a fading time $\tau_{f}$ during which satellites go from gas-rich and star-forming to gas-poor and quiescent. We find $0.7< \tau_{d}< 3$ Gyr at $z=0$, and depends inversely on the satellite halo mass at infall. At z ~ 1 we find ~$0.3< \tau_{d} < 2$ Gyr, broadly consistent with a positive correlation with the Hubble time. For a given halo mass, lower stellar mass galaxies at infall time have higher $\tau_{d}$. We generally find $\tau_{f}\ll \tau_{d}$, ranging between ~ 150 Myr at z~0 and ~ 80 Myr at z ~ 1 based on linear interpolation, with some uncertainty because they are smaller than our simulation output frequency ($200-300$ Myr). $\tau_{f}$ has no obvious dependency on infall halo mass. Both timescales show little difference between HI depletion and SF quenching, indicating that using up the gas reservoir by star formation without refilling is the main mechanism to transform satellite galaxies at these halo masses. At a given physical distance from the center of the main halo of interest, higher redshift galaxies have on average higher cold gas content, but the ratio of gas (HI or H$_2$) to star formation rate is similar, indicating that star formation is consistently fed through reservoirs of HI then H$_2$. For a given amount of HI, galaxies have shorter consumption times in more massive halo structures.

Ultra-diffuse Galaxies at Ultraviolet Wavelengths

Abstract We measure near-ultraviolet (NUV) aperture magnitudes from Galaxy Evolution Explorer images for 258 ultra-diffuse galaxy (UDG) candidates drawn from the initial Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) survey of ∼300 square degrees surrounding, and including, the Coma galaxy cluster. For the vast majority, 242 of them, we present flux upper limits due either to a lack of significant flux in the aperture or confusion with other objects projected within the aperture. These limits often place interesting constraints on the UDG candidates, indicating that they are non-star-forming or quiescent. In particular, we identify field, quiescent UDG candidates, which are a challenge for formation models and are, therefore, compelling prospects for spectroscopic follow-up and distance determinations. We present far-ultraviolet (FUV) and NUV magnitudes for 16 detected UDG candidates and compare those galaxies to the local population of galaxies on color–magnitude and specific star formation rate diagrams. The NUV-detected UDG candidates form mostly an extension toward lower stellar masses of the star-forming galaxy sequence, and none of these lie within regions of high local galaxy density. UDG candidates span a range of properties, although almost all are consistent with being quiescent, low surface brightness galaxies, regardless of environment.

Galaxies of the z ∼ 2 Universe. I. Grism-selected Rest-frame Optical Emission-line Galaxies

Abstract Euclid, the Wide Field Infrared Survey Telescope, and the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) will make emission-line selected galaxies the largest observed constituent in the z &gt; 1 universe. However, we only have a limited understanding of the physical properties of galaxies selected via their Lyα or rest-frame optical emission lines. To address this problem, we present the basic properties of ∼2000 All-Wavelength Extended Groth Strip International Survey, Cosmological Evolution Survey, Great Observatories Origins Deep Survey-North, Great Observatories Origins Deep Survey-South, and Ultra Deep Survey galaxies identified in the redshift range 1.90 &lt; z &lt; 2.35 via their [O ii], Hβ, and [O iii] emission lines in the 3D-Hubble Space Telescope survey. For these z ∼ 2 galaxies, [O iii] is generally much brighter than [O ii] and Hβ, with typical rest-frame equivalent widths of several hundred Angstroms. Moreover, these strong emission-line systems span an extremely wide range of stellar mass (∼3 dex), star formation rate (∼2 dex), and [O iii] luminosity (∼2 dex). Comparing the distributions of these properties to those of continuum-selected galaxies, we find that emission-line galaxies have systematically lower stellar masses and lower optical/UV dust attenuations. These measurements lay the groundwork for an extensive comparison between these rest-frame optical emission-line galaxies and Lyα emitters identified in the HETDEX survey.

Emission-line Metallicities from the Faint Infrared Grism Survey and VLT/MUSE

Abstract We derive direct-measurement gas-phase metallicities of for 14 low-mass emission-line galaxies at 0.3 &lt; z &lt; 0.8 identified in the Faint Infrared Grism Survey. We use deep slitless G102 grism spectroscopy of the Hubble Ultra Deep Field, dispersing light from all objects in the field at wavelengths between 0.85 and 1.15 μm. We run an automatic search routine on these spectra to robustly identify 71 emission-line sources, using archival data from Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) to measure additional lines and confirm redshifts. We identify 14 objects with 0.3 &lt; z &lt; 0.8 with measurable [O iii]λ4363 Å emission lines in matching VLT/MUSE spectra. For these galaxies, we derive direct electron-temperature gas-phase metallicities with a range of . With matching stellar masses in the range of 107.9 M ⊙ &lt; M ⋆ &lt; 1010.4 M ⊙, we construct a mass–metallicity (MZ) relation and find that the relation is offset to lower metallicities compared to metallicities derived from alternative methods (e.g., R 23, O3N2, N2O2) and continuum selected samples. Using star formation rates derived from the Hα emission line, we calculate our galaxies’ position on the Fundamental Metallicity Relation, where we also find an offset toward lower metallicities. This demonstrates that this emission-line-selected sample probes objects of low stellar masses but even lower metallicities than many comparable surveys. We detect a trend suggesting galaxies with higher Specific Star Formation (SSFR) are more likely to have lower metallicity. This could be due to cold accretion of metal-poor gas that drives star formation, or could be because outflows of metal-rich stellar winds and SNe ejecta are more common in galaxies with higher SSFR.

Distinguishing Mergers and Disks in High-redshift Observations of Galaxy Kinematics

Abstract The majority of massive star-forming galaxies at z ∼ 2 have velocity gradients suggestive of rotation, in addition to large amounts of disordered motions. In this paper, we demonstrate that it is challenging to distinguish the regular rotation of a disk galaxy from the orbital motions of merging galaxies with seeing-limited data. However, the merger fractions at z ∼ 2 are likely too low for this to have a large effect on measurements of disk fractions. To determine how often mergers pass for disks, we look to galaxy formation simulations. We analyze ∼24,000 synthetic images and kinematic maps of 31 high-resolution simulations of isolated galaxies and mergers at z ∼ 2. We determine if the synthetic observations pass the criteria commonly used to identify disk galaxies and whether the results are consistent with their intrinsic dynamical states. Galaxies that are intrinsically mergers pass the disk criteria for anywhere from 0% to 100% of sightlines. The exact percentage depends strongly on the specific disk criteria adopted and weakly on the separation of the merging galaxies. Therefore, one cannot tell with certainty whether observations of an individual galaxy indicate a merger or a disk. To estimate the fraction of mergers passing as disks in current kinematics samples, we combine the probability that a merger will pass as a disk with theoretical merger fractions from a cosmological simulation. Taking the latter at face value, the observed disk fractions are overestimated by small amounts: at most by 5% at high stellar mass (1010–11 M ⊙) and 15% at low stellar mass (109–10 M ⊙).

A systematic metallicity study of DustPedia galaxies reveals evolution in the dust-to-metal ratios

Observations of evolution in the dust-to-metal ratio allow us to constrain the dominant dust processing mechanisms. In this work, we present a study of the dust-to-metal and dust-to-gas ratios in a sub-sample of ~500 DustPedia galaxies. Using literature and MUSE emission line fluxes, we derived gas-phase metallicities (oxygen abundances) for over 10 000 individual regions and determine characteristic metallicities for each galaxy. We study how the relative dust, gas, and metal contents of galaxies evolve by using metallicity and gas fraction as proxies for evolutionary state. The global oxygen abundance and nitrogen-to-oxygen ratio are found to increase monotonically as galaxies evolve. Additionally, unevolved galaxies (gas fraction &gt;60%, metallicity 12 + log(O∕H) &lt; 8.2) have dust-to-metal ratios that are about a factor of 2.1 lower (a factor of six lower for galaxies with gas fraction &gt;80%) than the typical dust-to-metal ratio (Md∕MZ ~ 0.214) for more evolved sources. However, for high gas fractions, the scatter is larger due to larger observational uncertainties as well as a potential dependence of the dust grain growth timescale and supernova dust yield on local conditions and star formation histories. We find chemical evolution models with a strong contribution from dust grain growth describe these observations reasonably well. The dust-to-metal ratio is also found to be lower for low stellar masses and high specific star formation rates (with the exception of some sources undergoing a starburst). Finally, the metallicity gradient correlates weakly with the HI-to-stellar mass ratio, the effective radius and the dust-to-stellar mass ratio, but not with stellar mass.

Confirming Herschel Candidate Protoclusters from ALMA/VLA CO Observations

Abstract ALMA 870 μm continuum imaging has uncovered a population of blends of multiple dusty star-forming galaxies (DSFGs) in sources originally detected with the Herschel Space Observatory. However, their pairwise separations are much smaller than what is found by ALMA follow-up of other single-dish surveys or expected from theoretical simulations. Using ALMA and the Very Large Array, we have targeted three of these systems to confirm whether the multiple 870 μm continuum sources lie at the same redshift, successfully detecting 12CO (J = 3–2) and 12CO (J = 1–0) lines and being able to confirm that in the three cases all the multiple DSFGs are likely physically associated within the same structure. Therefore, we report the discovery of two new gas-rich dusty protocluster cores (HELAISS02, z = 2.171 ± 0.004; HXMM20, z = 2.602 ± 0.002). The third target is located in the well-known COSMOS overdensity at z = 2.51 (named CL J1001+0220 in the literature), for which we do not find any new secure CO (1–0) detection, although some of its members show only tentative detections and require further confirmation. From the gas, dust, and stellar properties of the two new protocluster cores, we find very large molecular gas fractions yet low stellar masses, pushing the sources above the main sequence (MS), while not enhancing their star formation efficiency. We suggest that the sources might be newly formed galaxies migrating to the MS. The properties of the three systems compared to each other and to field galaxies may suggest a different evolutionary stage between systems.

Quiescent Galaxy Size and Spectroscopic Evolution: Combining HSC Imaging and Hectospec Spectroscopy

Abstract We explore the relationships between size, stellar mass, and average stellar population age (indicated by D n 4000 indices) for a sample of ∼11,000 intermediate-redshift galaxies from the SHELS spectroscopic survey (Geller et al. 2014) augmented by high-resolution Subaru Telescope Hyper Suprime-Cam imaging. In the redshift interval 0.1 &lt; z &lt; 0.6, star-forming galaxies are on average larger than their quiescent counterparts. The mass-complete sample of ∼3500 quiescent galaxies shows that the average size of a quiescent galaxy increases by ≲25% from z ∼ 0.6 to z ∼ 0.1. This growth rate is a function of stellar mass: the most massive ( ) galaxies grow significantly more slowly in size than quiescent systems an order of magnitude less massive that grow by 70% in the 0.1 ≲ z ≲ 0.3 redshift interval. For galaxies, age and size are anticorrelated at fixed mass; more massive quiescent systems show no significant trend in size with average stellar population age. The evolution in absolute and fractional abundances of quiescent systems at intermediate redshift are also a function of galaxy stellar mass. The suite of evolutionary trends suggests that galaxies more massive than have mostly assembled their mass by z ∼ 0.6. Quiescent galaxies with lower stellar masses show more complex evolution that is characterized by a combination of individual quiescent galaxy size growth (through mergers) and an increase in the size of newly quenched galaxies joining the population at later times (progenitor bias). The low-mass population ( ) grows predominantly as a result of progenitor bias. For more massive ( ) quiescent galaxies, (predominantly minor) mergers and progenitor bias make more comparable contributions to the size growth. At intermediate redshift, quiescent size growth is mass-dependent; the most massive ( ) galaxies experience the least rapid increase in size from z ∼ 0.6 to z ∼ 0.1.

HST F160W Imaging of Very Massive Galaxies at 1.5 &lt; z &lt; 3.0: Diversity of Structures and the Effect of Close Pairs on Number Density Estimates

Abstract We present a targeted follow-up Hubble Space Telescope WFC3 F160W imaging study of very massive galaxies ( ) selected from a combination of ground-based near-infrared galaxy surveys (UltraVISTA, NEWFIRM Medium Band Survey-II , UKIRT Infrared Deep Sky Survey (UKIDSS) Ultra-Deep Survey (UDS) at 1.5 &lt; z &lt; 3). We find that these galaxies are diverse in their structures, with ∼1/3 of the targets being composed of close pairs, and span a wide range in sizes. At 1.5 &lt; z &lt; 2.5, the sizes of both star-forming and quiescent galaxies are consistent with the extrapolation of the stellar mass–size relations determined at lower stellar masses. At 2.5 &lt; z &lt; 3.0, however, we find evidence that quiescent galaxies are systematically larger than expected based on the extrapolation of the relation derived using lower stellar mass galaxies. We used the observed light profiles of the blended systems to decompose their stellar masses and investigate the effect of the close pairs on the measured number densities of very massive galaxies in the early universe. We estimate correction factors to account for close-pair blends and apply them to the observed stellar mass functions (SMFs) measured using ground-based surveys. Given the large uncertainties associated with this extreme population of galaxies, there is currently little tension between the (blending-corrected) number density estimates and predictions from theoretical models. Although we currently lack the statistics to robustly correct for close-pair blends, we show that this is a systematic effect that can reduce the observed number density of very massive galaxies by up to a factor of ∼1.5, and should be accounted for in future studies of SMFs.

The Galaxy–Halo Connection in Low-mass Halos

Abstract Properties of galaxies vary systematically with the mass of their parent dark matter halos. This basic galaxy–halo connection shows a fair amount of scatter whose origin is not fully understood. Here, we study how differences in the halo assembly history affect central galaxies in low-mass (M halo &lt; 1012 M ⊙) halos at z = 2–6 with the help of the MassiveFIRE suite of cosmological simulations. In contrast to previous works that tie galaxy properties to halo concentration and halo-formation redshift, we focus on halo growth rate as a measure of assembly history. We find that, at fixed halo mass, faster-growing halos tend to have lower stellar masses and higher star formation rates (SFRs) per unit stellar mass but similar overall SFRs. We provide a simple explanation for these findings with the help of an analytic model that captures approximately the behavior of our hydrodynamical simulations. Specifically, among halos of a given current mass, quickly growing halos have lower stellar masses (and thus higher specific SFRs) because they were less massive and had comparably lower cold-gas masses and SFRs in the past than slowly growing halos. By combining these findings with estimates for the scatter of the halo growth rate, we show that variations in growth rate at fixed halo mass may largely explain the scatter of the stellar mass–halo mass relation. In contrast, halo growth variations likely play only a minor role in the scatter of the star-forming sequence in low-mass galaxies.

Possible evidence of the radio AGN quenching of neighbouring galaxies atz∼ 1

Using 57 Radio Active Galactic nuclei (RAGN) at 0.55 $\leq$ z $\leq$ 1.3 drawn from five fields of the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey, we study the effect of injection of energy from outbursts of RAGN on their spectroscopically-confirmed neighboring galaxies (SNGs). We observe an elevated fraction of quenched neighbors (fq) within 500 kpc projected radius of RAGN in the most dense local environments compared to those of non-RAGN control samples matched to the RAGN population in colour, stellar mass, and local environment at 2$\sigma$ significance. Further analyses show that there are offsets at similar significance between fqs of RAGN-SNGs and the appropriate control samples for galaxies specifically in cluster environments and those hosted by most massive cluster galaxies, which tentatively suggests that some negative feedback from the RAGN is occurring in these dense environments. In addition, we find that the median radio power of RAGN increases with increasing local overdensity, an effect which may lend itself to the quenching of neighboring galaxies. Furthermore, we find that, in the highest local overdensities, the fq of the sub-sample of lower stellar mass RAGN-SNGs is larger than that of the higher stellar mass RAGN-SNGs sub-sample, which indicates a more pronounced effect from RAGN on lower stellar mass galaxies. We propose a scenario in which RAGN residing within clusters might heat the intracluster medium (ICM) affecting both in situ star formation and any inflowing gas that remains in their neighboring galaxies.

Suppression of Low-mass Galaxy Formation around Quasars at z ∼ 2–3

Abstract We have carried out deep and wide field imaging observations with narrow bands, targeting 11 quasar fields to systematically study the possible photoevaporation effect of quasar radiation on surrounding low mass galaxies at z ∼ 2–3. We focused on Lyα emitters (LAEs) at the same redshifts as quasars that lie within the quasar proximity zones, where the UV radiation from the quasars is higher than the average background at that epoch. We found that LAEs with high rest-frame equivalent width of Lyα emission (EW0) of ≳150 Å with low stellar mass (≲108 M ⊙) are predominantly scarce in the quasar proximity zones, suggesting that quasar photoevaporation effects may be taking place. The halo mass of LAEs with EW0 &gt; 150 Å is estimated to be either from spectral energy distribution fitting or the main sequence. Based on a hydrodynamical simulation, the predicted delay in star formation under a local UV background intensity with erg s−1 cm−2 Hz−1 sr−1 for galaxies having less than this halo mass is about &gt;20 Myr, which is longer than the expected age of LAEs with EW0 &gt; 150 Å. On the other hand, photoevaporation seems to be less effective around very luminous quasars, which is consistent with the idea that these are still in an early stage of activity.

Star-forming galaxies at low-redshift in the SHARDS survey

Context. The physical processes driving the evolution of star formation (SF) in galaxies over cosmic time still present many open questions. Recent galaxy surveys allow now to study these processes in great detail at intermediate redshift (0 ≤ z ≤ 0.5). Aims. We build a complete sample of star-forming galaxies and analyze their properties, reaching systems with low stellar masses and low star formation rates (SFRs) at intermediate-to-low redshift. Methods. We use data from the SHARDS multiband survey in the GOODS-North field. Its depth (up to magnitude ⟨m3σ⟩~ 26.5) and its spectro-photometric resolution (R ~ 50) provides us with an ideal dataset to search for emission line galaxies (ELGs). We develop a new algorithm to identify low-redshift (z &lt; 0.36) ELGs by detecting the [OIII]5007 and Hα emission lines simultaneously. We fit the spectral energy distribution (SED) of the selected sample, using a model with two single stellar populations. Results. We find 160 star-forming galaxies for which we derive equivalent widths (EWs) and absolute fluxes of both emission lines. We detect EWs as low as 12 Å, with median values for the sample of ~35 Å in [OIII]5007 and ~56 Å in Hα, respectively. Results from the SED fitting show a young stellar population with low median metallicity (36% of the solar value) and extinction (AV ~ 0.37), with median galaxy stellar mass ~108.5 M⊙. Gas-phase metallicities measured from available spectra are also low. ELGs in our sample present bluer colours in the UVJ plane than the median colour-selected star-forming galaxy in SHARDS. We suggest a new V-J colour criterion to separate ELGs from non-ELGs in blue galaxy samples. In addition, several galaxies present high densities of O-type stars, possibly producing galactic superwinds, which makes them interesting targets for follow-up spectroscopy. Conclusions. We have demonstrated the efficiency of SHARDS in detecting low-mass ELGs (~2 magnitudes deeper than previous spectroscopic surveys in the same field). The selected sample accounts for 20% of the global galaxy population at this redshift and luminosity, and is characterized by young SF bursts with sub-solar metallicities and low extinction. However, robust fits to the full SEDs can only be obtained including an old stellar population, suggesting the young component is built up by a recent burst of SF in an otherwise old galaxy.

OUP accepted manuscript

We investigate the binarity properties in field stars using more than 50\,000 main-sequence stars with stellar mass from 0.4 to 0.85\,$M_\odot$ observed by LAMOST and {\emph Gaia} in the solar neighborhood. By adopting a power-law shape of the mass-ratio distribution with power index of $\gamma$, we conduct a hierarchical Bayesian model to derive the binary fraction ($f_{b}$) and $\gamma$ for stellar populations with different metallicities and primary masses ($m_1$). We find that $f_b$ is tightly anti-correlated with $\gamma$, i.e. the populations with smaller binary fraction contains more binaries with larger mass-ratio and vice versa.The high-$\gamma$ populations with $\gamma>1.2$ have lower stellar mass and higher metallicity, while the low-$\gamma$ populations with $\gamma<1.2$ have larger mass or lower metallicity. The $f_b$ of the high-$\gamma$ group is anti-correlated with [Fe/H] but flat with $m_1$.Meanwhile, the $f_b$ of the low-$\gamma$ group displays clear correlation with $m_1$ but quite flat with [Fe/H]. The substantial differences are likely due to the dynamical processing when the binaries were in the embedded star clusters in their early days. The dynamical processing tends to destroy binaries with smaller primary mass, smaller mass-ratio, and wider separation. Consequently, the high-$\gamma$ group containing smaller $m_1$ is more effectively influenced and hence contains less binaries, many of which have larger mass-ratio and shorter period. However, the low-$\gamma$ group is less affected by the dynamical processing due to their larger $m_1$. These are evident that the dynamical processing does effectively work and significantly reshape the present-day binary properties of field stars.

Age, metallicity, and star formation history of spheroidal galaxies in cluster atz∼ 1.2

We present the analysis, based on spectra collected at the Large Binocular Telescope, of the stellar populations in seven spheroidal galaxies in the cluster XLSSJ0223 at $z$$\sim$1.22. The aim is to constrain the epoch of their formation and their star formation history. Using absorption line strenghts and full spectral fitting, we derive for the stellar populations of the seven spheroids a median age <Age>=2.4$\pm$0.6 Gyr, corresponding to a median formation redshift $<$$z_f$$>$$\sim2.6_{-0.5}^{+0.7}$ (lookback time = 11$_{-1.0}^{+0.6}$ Gyr). We find a significant scatter in age, showing that massive spheroids, at least in our targeted cluster, are not coeval. The median metallicity is [Z/H]=0.09$\pm$0.16, as for early-types in clusters at 0$<$$z$<0.9. This lack of evolution of [Z/H] over the range 0$<$$z$$<$1.3, corresponding to the last 9 billions years, suggests that no significant additional star formation and chemical enrichment are required for cluster spheroids to reach the present-day population. We do not detect significant correlation between age and velocity dispersion $\sigma_e$, or dynamical mass M$_{dyn}$, or effective stellar mass density $\Sigma_e$. On the contrary, the metallicity [Z/H] of the seven spheroids is correlated to their dynamical mass M$_{dyn}$, according to a relation similar to the one for local spheroids. [Z/H] is also anticorrelated to stellar mass density $\Sigma_e$ because of the anticorrelation between M$_{dyn}$ and $\Sigma_e$. Therefore, the basic trends observed in the local universe were already established at $z\sim1.3$, i.e. more massive spheroids are more metal rich, have lower stellar mass density and tend to be older than lower-mass galaxies.

Systematically Measuring Ultra-diffuse Galaxies (SMUDGes). I. Survey Description and First Results in the Coma Galaxy Cluster and Environs

Abstract We present a homogeneous catalog of 275 large (effective radius ≳5.″3) ultra-diffuse galaxy (UDG) candidates lying within an ≈290 square degree region surrounding the Coma Cluster. The catalog results from our automated postprocessing of data from the Legacy Surveys, a three-band imaging survey covering 14,000 square degrees of the extragalactic sky. We describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma Cluster. We conclude that the majority of our detections are at roughly the distance of the Coma Cluster, implying effective radii ≥2.5 kpc, and that our sample contains a significant number of analogs of DF44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field. The g − z color of our UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but we find both red and blue UDG candidates in the vicinity of the Coma Cluster and a relative overabundance of blue UDG candidates in the lower-density environments and the field. Our eventual processing of the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.

Expected intermediate mass black holes in the Virgo cluster. II. Late-type galaxies

The Chandra X-ray Observatory's Cycle 18 Large Program titled "Spiral galaxies of the Virgo Cluster" will image 52 galaxies with the ACIS-S detector. Combined with archival data for an additional 22 galaxies, this will represent the complete sample of 74 spiral galaxies in the Virgo cluster with star-formation rates $\gtrsim$ 0.3 $M_{\odot}$/yr. Many of these galaxies are expected to have an active nucleus, signalling the presence of a central black hole. In preparation for this survey, we predict the central black hole masses using the latest black hole scaling relations based on spiral arm pitch angle $\phi$, velocity dispersion $\sigma$, and total stellar mass $M_{\rm *,galaxy}$. With a focus on intermediate mass black holes ($10^2<M_{\rm bh}/M_{\odot}<10^5$), we highlight NGC 4713 and NGC 4178, both with $M_{\rm bh}\approx10^3$-$10^4$ (an estimate which is further supported in NGC 4178 by its nuclear star cluster mass). From Chandra archival data, we find that both galaxies have a point-like nuclear X-ray source, with unabsorbed 0.3-10 keV luminosities of a few times 10$^{38}$ erg/s. In NGC 4178, the nuclear source has a soft, probably thermal, spectrum consistent with a stellar-mass black hole in the high/soft state, while no strong constraints can be derived for the nuclear emission of NGC 4713. In total, 33 of the 74 galaxies are predicted to have $M_{\rm bh}<(10^5$-$10^6)$ $M_{\odot}$, and several are consistently predicted, via three methods, to have masses of $10^4$-$10^5\,M_{\odot}$, such as IC 3392, NGC 4294 and NGC 4413. We speculate that a sizeable population of IMBHs may reside in late-type spiral galaxies with low stellar mass ($M_{\rm *,galaxy}\lesssim10^{10}\,M_{\odot}$).

J1234+3901: an extremely metal-deficient compact star-forming dwarf galaxy at redshift 0.133

We have obtained optical spectroscopy of one of the most metal-poor dwarf star-forming galaxies (SFG) in the local Universe, J1234+3901, with the Large Binocular Telescope (LBT)/Multi-Object Dual Spectrograph (MODS). This blue compact dwarf (BCD) galaxy with a redshift z=0.133 was selected from the Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS). Its properties are extreme in many ways. Its oxygen abundance 12 + log O/H = 7.035+/-0.026 is among the lowest ever observed for a SFG. Its absolute magnitude Mg = -17.35 mag makes it the brightest galaxy among the known BCDs with 12 + log O/H < 7.3. With its low metallicity, low stellar mass M* = 10^7.13 Msun and very low mass-to-light ratio M*/Lg ~ 0.01 (in solar units), it deviates strongly from the mass-metallicity and luminosity-metallicity relations defined by the bulk of the SFGs in SDSS DR14. J1234+3901 has a very high specific star-formation rate sSFR ~ 100 Gyr^-1, indicating very active ongoing star-formation. Its spectrum shows a strong HeII 4686 emission line, with a flux ~ 2.4 per cent that of the Hbeta emission line. The most probable source of ionizing radiation for producing such a strong line is fast radiative shocks. J1234+3901 has a ratio O32 = [OIII]5007/[OII]3727 ~ 15, the highest among the lowest-metallicity SFGs, and is thus likely leaking Lyman continuum radiation. It is a good candidate for being a young dwarf galaxy, with a large fraction of its stars formed recently. As such, it is probably one of the best local counterparts of dwarf primeval galaxies responsible for the reionization of the early Universe.

The MOSDEF Survey: Significant Evolution in the Rest-frame Optical Emission Line Equivalent Widths of Star-forming Galaxies at z = 1.4–3.8

Abstract We use extensive spectroscopy from the MOSFIRE Deep Evolution Field survey to investigate the relationships between rest-frame optical emission line equivalent widths (W) and a number of galaxy and interstellar medium (ISM) characteristics for a sample of 1134 star-forming galaxies at redshifts 1.4 ≲ z ≲ 3.8. We examine how the equivalent widths of , , λλ4960, 5008, + Hβ, , and , depend on stellar mass, UV slope, age, star formation rate (SFR) and specific SFR (sSFR), ionization parameter and excitation conditions (O32 and /Hβ), gas-phase metallicity, and ionizing photon production efficiency (ξ ion). The trend of increasing W with decreasing stellar mass is strongest for (and +Hβ). More generally, the equivalent widths of all the lines increase with redshift at a fixed stellar mass or fixed gas-phase metallicity, suggesting that high equivalent width galaxies are common at high redshift. This redshift evolution in equivalent widths can be explained by the increase in SFR and decrease in metallicity with redshift at a fixed stellar mass. Consequently, the dependence of W on sSFR is largely invariant with redshift, particularly when examined for galaxies of a given metallicity. Our results show that high equivalent width galaxies, specifically those with high , have low stellar masses, blue UV slopes, young ages, high sSFRs, ISM line ratios indicative of high ionization parameters, high ξ ion, and low metallicities. As these characteristics are often attributed to galaxies with high ionizing escape fractions, galaxies with high W are likely candidates for the population that dominates cosmic reionization.

Optical integral field spectroscopy observations applied to simulated galaxies: testing the fossil record method

By means of post-processed cosmological Hydrodynamics simulations we explore the ability of the fossil record method to recover the stellar mass, age gradients, and global/radial star formation and mass growth histories of galaxies observed with an optical Integral Field Unity. We use two simulations of representative Milky Way-sized galaxies, one disk dominated and another bulge-dominated. We generate data cubes emulating MaNGA/SDSS-IV instrumental and observational conditions, and analyze them using the Pipe3D pipeline. For optimal MaNGA instrumental/observational setups, the global masses, ages, and dust extinctions of both galaxies are well recovered within the uncertainties, while for the radial distributions, the trend is to get slightly flatter age gradients and weaker inside-out growth modes than the true ones. The main bias is in recovering younger stellar populations in the inner, older regions, and slightly older stellar populations in the outer, younger regions, as well as lower global stellar masses. These trends are enhanced as lower is the spatial sampling/resolution (less number of fibers), more inclined and dust-attenuated is the observed galaxy, lower is the signal-to-noise ratio, and worse is the seeing. The recovered properties and histories are more affected for the disk-dominated galaxy with a prominent inside-out growth mode than for the bulge-dominated galaxy assembled earlier and more coherently. We make publicly available the code and the mock IFU datacubes used in this paper.