Main Galaxy Research Articles

ADDGALS: Simulated Sky Catalogs for Wide Field Galaxy Surveys

We present a method for creating simulated galaxy catalogs with realistic galaxy luminosities, broadband colors, and projected clustering over large cosmic volumes. The technique, denoted Addgals (Adding Density Dependent GAlaxies to Lightcone Simulations), uses an empirical approach to place galaxies within lightcone outputs of cosmological simulations. It can be applied to significantly lower-resolution simulations than those required for commonly used methods such as halo occupation distributions, subhalo abundance matching, and semi-analytic models, while still accurately reproducing projected galaxy clustering statistics down to scales of r ∼ 100 h −1kpc . We show that Addgals catalogs reproduce several statistical properties of the galaxy distribution as measured by the Sloan Digital Sky Survey (SDSS) main galaxy sample, including galaxy number densities, observed magnitude and color distributions, as well as luminosity- and color-dependent clustering. We also compare to cluster–galaxy cross correlations, where we find significant discrepancies with measurements from SDSS that are likely linked to artificial subhalo disruption in the simulations. Applications of this model to simulations of deep wide-area photometric surveys, including modeling weak-lensing statistics, photometric redshifts, and galaxy cluster finding, are presented in DeRose et al., and an application to a full cosmology analysis of Dark Energy Survey (DES) Year 3 like data is presented in DeRose et al. We plan to publicly release a 10,313 square degree catalog constructed using Addgals with magnitudes appropriate for several existing and planned surveys, including SDSS, DES, VISTA, Wide-field Infrared Survey Explorer, and Rubin Observatory’s Legacy Survey of Space and Time.

Strong spiral arms drive secular growth of pseudo bulges in disk galaxies

Spiral-driven instabilities may drive gas inflow to enhance central star formation in disk galaxies. We investigate this hypothesis using the Sloan Digital Sky Survey (SDSS) in a sample of 2779 nearby unbarred star-forming main sequence spiral galaxies. The strength of spiral arms is quantified by their average Fourier amplitude relative to the axisymmetric disk. The star formation properties in the central 1–3 kpc region were derived from the SDSS spectra. We show that galaxies with stronger spiral arms not only tend to have more intense central specific star formation rates (sSFRs), larger Balmer absorption line indices, and lower 4000 Å break strengths, but also have enhanced central sSFRs relative to the sSFR measured for the whole galaxy. This link is independent of redshift, stellar mass, surface density, and concentration. There is a lack of evidence for strong spiral arms being associated with a significant fraction of starburst or post-starburst galaxies, implying that the spiral-induced central star formation is likely continuous rather than bursty. We also show that stronger spiral arms tend to have an increasing fraction of pseudo bulges, a relatively unchanged fraction of star-forming classical bulges, and a decreasing fraction of quenched classical bulges. Moreover, the concentration of galaxies hosting pseudo bulges mildly increases with stronger spiral arms, implying that spirals help pseudo bulges grow. The connection between spirals and bulge type is partly attributed to the suppression of spirals by classical bulges and partly to the enhanced central star formation driven by spirals. We explain our results in the context of a scenario where spiral arms transport cold gas inward to trigger continuous central star formation, which facilitates the buildup of pseudo bulges. Spiral arms thus play a role in the secular evolution of disk galaxies.

Multiwavelength and Multi-CO View of the Minor Merger Driven Star Formation in the Nearby LIRG NGC 3110

We present Atacama Large Millimeter/submillimeter Array observations of multiple 12CO, 13CO, and C18O lines and 2.9 mm and 1.3 mm continuum emission toward the nearby interacting luminous infrared galaxy NGC 3110, supplemented with similar spatial resolution Hα, 1.4 GHz continuum, and K-band data. We estimate the typical CO-to-H2 conversion factor of 1.7 M ⊙ (K km s−1 pc2)−1 within the disk using local thermal equilibrium-based and dust-based H2 column densities, and measure the 1 kpc scale surface densities of the star formation rate (ΣSFR), super star clusters (ΣSSC), molecular gas mass, and star formation efficiency (SFE) toward the entire gas disk. These parameters show a peak in the southern part of the southern spiral arm (SFE ∼ 10−8.2 yr−1, ΣSFR ∼ 10−0.6 M ⊙ kpc−2 yr−1, ΣSSC ∼ 6.0 kpc−2), which is likely attributable to the ongoing tidal interaction with the companion galaxy MCG-01-26-013, as well as toward the circumnuclear region. We also find that thermal free–free emission contributes to a significant fraction of the millimeter continuum emission at the position of the southern peak. These measurements imply that the peak of the southern arm is an active and young star-forming region, whereas the central part of NGC 3110 is a site of long-continued star formation. We suggest that during the early stage of the galaxy–galaxy interaction in which the mass ratio was high in NGC 3110, fragmentation along the main galaxy arms is an important driver of merger-induced star formation, and that massive gas inflow results in dusty nuclear starbursts.

The velocity structure of the intracluster medium of the Centaurus cluster

ABSTRACT There are few direct measurements of the intracluster medium (ICM) velocity structure, despite its importance for understanding clusters. We present a detailed analysis of the velocity structure of the Centaurus cluster using XMM–Newton observations. Using a new European Photon Imaging Camera-pn energy scale calibration, which uses the Cu Kα instrumental line as reference, we are able to obtain velocity measurements with uncertainties down to Δ$\mathit{ v}$ ∼ 79 km s−1. We create 2D spectral maps for the velocity, metallicity, temperature, density, entropy, and pressure with a spatial resolution of 0.25 arcmin. We have found that the velocity structure of the ICM is similar to the velocity structure of the main galaxies, while the cold fronts are likely moving in a plane perpendicular to our line of sight with low velocity. Finally, we have found a contribution from the kinetic component of $\lt 25{{\ \rm per\ cent}}$ to the total energetic budget for a radius >30 kpc.

Warm Dark Matter Galaxies with Central Supermassive Black Holes

We generalize the Thomas–Fermi approach to galaxy structure to include central supermassive black holes and find, self-consistently and non-linearly, the gravitational potential of the galaxy plus the central black hole (BH) system. This approach naturally incorporates the quantum pressure of the fermionic warm dark matter (WDM) particles and shows its full power and clearness in the presence of supermassive black holes. We find the main galaxy and central black hole magnitudes as the halo radius rh, halo mass Mh, black hole mass MBH, velocity dispersion σ, and phase space density, with their realistic astrophysical values, masses and sizes over a wide galaxy range. The supermassive black hole masses arise naturally in this framework. Our extensive numerical calculations and detailed analytic resolution of the Thomas–Fermi equations show that in the presence of the central BH, both DM regimes—classical (Boltzmann dilute) and quantum (compact)—do necessarily co-exist generically in any galaxy, from the smaller and compact galaxies to the largest ones. The ratio R(r) of the particle wavelength to the average interparticle distance shows consistently that the transition, R≃1, from the quantum to the classical region occurs precisely at the same point rA where the chemical potential vanishes. A novel halo structure with three regions shows up: in the vicinity of the BH, WDM is always quantum in a small compact core of radius rA and nearly constant density; in the region rA<r<ri until the BH influence radius ri, WDM is less compact and exhibits a clear classical Boltzmann-like behavior; for r>ri, the WDM gravity potential dominates, and the known halo galaxy shows up with its astrophysical size. DM is a dilute classical gas in this region. As an illustration, three representative families of galaxy plus central BH solutions are found and analyzed: small, medium and large galaxies with realistic supermassive BH masses of 105M⊙, 107M⊙ and 109M⊙, respectively. In the presence of the central BH, we find a minimum galaxy size and mass Mhmin≃107M⊙, larger (2.2233×103 times) than the one without BH, and reached at a minimal non-zero temperature Tmin. The supermassive BH heats up the DM and prevents it from becoming an exactly degenerate gas at zero temperature. Colder galaxies are smaller, and warmer galaxies are larger. Galaxies with a central black hole have large masses Mh>107M⊙>Mhmin; compact or ultracompact dwarf galaxies in the range 104M⊙<Mh<107M⊙ cannot harbor central BHs. We find novel scaling relations MBH=DMh38 and rh=CMBH43, and show that the DM galaxy scaling relations Mh=bΣ0rh2 and Mh=aσh4/Σ0 hold too in the presence of the central BH, Σ0 being the constant surface density scale over a wide galaxy range. The galaxy equation of state is derived: pressure P(r) takes huge values in the BH vicinity region and then sharply decreases entering the classical region, following consistently a self-gravitating perfect gas P(r)=σ2ρ(r) behavior.

Emergence of galactic morphologies at cosmic dawn: input from numerical modelling

ABSTRACTWe employ a series of high-resolution zoom-in cosmological simulations to analyse the emerging morphology of main galaxies in dark matter haloes at z ≳ 2. We choose haloes of similar masses, ${\rm log}\, M_{\rm vir}/{\rm M_\odot }\sim 11.65\pm 0.05$, at the target zf = 6, 4, and 2. The rationale for this choice allows us to analyse how the different growth rate in these haloes propagates down to galaxy scales, affecting their basic parameters. Halos were embedded in high/low overdensity regions, and two versions of a galactic wind feedback were employed. Our main results are: (1) Although our galaxies evolve in different epochs, their global parameters remain within narrow range. Their morphology, kinematics, and stellar populations differ substantially, yet all host sub-kpc stellar bars; (2) The star formation rates appear higher for larger zf; (3) Bulges and stellar spheroids were separated by stellar kinematics, discy bulges were revealed using the Sersic method and photometry.The bulge-to-total mass ratios appear independent of the last merger time for all zf. The spheroid-to-total mas ratios lie within ∼0.5–0.8; (4) The synthetic redshifted, pixelized, and PSF-degraded JWST images allow detection of stellar discs at all zf. (5) Based on the kinematic decomposition, rotational support in discs depends on the feedback type, but increases with decreasing zf; (6) Finally, the ALMA images detect discs at all zf, but spiral structure is detectable in zf = 2 galaxies. Moreover, galaxies follow the Tully–Fisher relation, being separated only by the galactic wind feedback.

The Hubble Constant from Strongly Lensed Supernovae with Standardizable Magnifications

Abstract The dominant uncertainty in the current measurement of the Hubble constant (H 0) with strong gravitational lensing time delays is attributed to uncertainties in the mass profiles of the main deflector galaxies. Strongly lensed supernovae (glSNe) can provide, in addition to measurable time delays, lensing magnification constraints when knowledge about the unlensed apparent brightness of the explosion is imposed. We present a hierarchical Bayesian framework to combine a data set of SNe that are not strongly lensed and a data set of strongly lensed SNe with measured time delays. We jointly constrain (i) H 0 using the time delays as an absolute distance indicator, (ii) the lens model profiles using the magnification ratio of lensed and unlensed fluxes on the population level, and (iii) the unlensed apparent magnitude distribution of the SN population and the redshift–luminosity relation of the relative expansion history of the universe. We apply our joint inference framework on a future expected data set of glSNe and forecast that a sample of 144 glSNe of Type Ia with well-measured time series and imaging data will measure H 0 to 1.5%. We discuss strategies to mitigate systematics associated with using absolute flux measurements of glSNe to constrain the mass density profiles. Using the magnification of SN images is a promising and complementary alternative to using stellar kinematics. Future surveys, such as the Rubin and Roman observatories, will be able to discover the necessary number of glSNe, and with additional follow-up observations, this methodology will provide precise constraints on mass profiles and H 0.

Observing Ram Pressure at Work in Intermediate Redshift Clusters with MUSE: The Case of Abell 2744 and Abell 370

Abstract Ram pressure stripping has been proven to be effective in shaping galaxy properties in dense environments at low redshift. The availability of Multi Unit Spectroscopic Explorer (MUSE) observations of a sample of distant (z ∼ 0.3–0.5) clusters has allowed one to search for galaxies subject to this phenomenon at significant lookback times. In this paper we describe how we discovered and characterized 13 ram-pressure-stripped galaxies in the central regions of two intermediate redshift (z ∼ 0.3–0.4) clusters, A2744 and A370, using the MUSE spectrograph. Emission-line properties as well as stellar features have been analyzed to infer the presence of this gas-only stripping mechanism, that produces spectacular ionized gas tails (Hα and even more astonishing [O ii](3727, 3729)) departing from the main galaxy body. The inner regions of these two clusters reveal the predominance of such galaxies among blue star-forming cluster members, suggesting that ram pressure stripping was even more effective at intermediate redshift than in today’s universe. Interestingly, the resolved [O ii]/Hα line ratio in the stripped tails is exceptionally high compared to that in the disks of these galaxies, (which is comparable to that in normal low-z galaxies), suggesting lower gas densities and/or an interaction with the hot surrounding intracluster medium.

A Self-Calibrating Halo-Based Group Finder: Application to SDSS

Abstract We apply a new galaxy group-finder to the Main Galaxy Sample of the SDSS. This algorithm introduces new freedom to assign halos to galaxies that is self-calibrated by comparing the catalog to complementary data. These include galaxy clustering data and measurements of the total satellite luminosity from deep-imaging data. We present constraints on the galaxy-halo connection for star-forming and quiescent populations. The results of the self-calibrated group catalog differ in several key ways from previous group catalogs and halo-occupation analyses. The transition halo mass scale, where half of the halos contain quiescent central galaxies, is at M h ∼ 1012.4 h −1 M ⊙, significantly higher than other constraints. Additionally, the width of the transition from predominantly star-forming halos to quiescent halos occurs over a narrower range in halo mass. Quiescent central galaxies in low-mass halos are significantly more massive than star-forming centrals at the same halo mass, but this difference reverses above the transition halo mass. We find that the scatter in log M * at fixed M h is ∼0.2 dex for massive halos, in agreement with previous estimates, but rises sharply at lower halo masses. The halo masses assigned by the group catalog are in good agreement with weak-lensing estimates for star-forming and quiescent central galaxies. We discuss possible improvements to the algorithm made clear by this first application to data. The group catalog is made publicly available.

SDSS-IV MaNGA: the physical origin of off-galaxy H α blobs in the local Universe

ABSTRACT H α blobs are off-galaxy emission-line regions with weak or no optical counterparts. They are mostly visible in H α line, appearing as concentrated blobs. Such unusual objects have been rarely observed and studied, and their physical origin is still unclear. We have identified 13 H α blobs in the public data of MaNGA survey, by visually inspecting both the optical images and the spatially resolved maps of H α line for ∼4600 galaxy systems. Among the 13 H α blobs, 2 were reported in previously MaNGA-based studies and 11 are newly discovered. This sample, though still small in size, is by far the largest sample with both deep imaging and integral field spectroscopy. Therefore, for the first time we are able to perform statistical studies to investigate the physical origin of H α blobs. We examine the physical properties of these H α blobs and their associated galaxies, including their morphology, environments, gas-phase metallicities, kinematics of ionized gas, and ionizing sources. We find that the H α blobs in our sample can be broadly divided into two groups. One is associated with interacting/merging galaxy systems, of which the ionization is dominated by shocks or diffuse ionized gas. It is likely that these H α blobs used to be part of their nearby galaxies, but were stripped away at some point due to tidal interactions. The other group is found in gas-rich systems, appearing as low-metallicity star-forming regions that are visually detached from the main galaxy. These H α blobs could be associated with faint discs, spiral arms, or dwarf galaxies.

Bridging the Gap Between Simply Parametrized and Free-Form Pixelated Models of Galaxy Lenses: The Case of WFI 2033-4723 Quad

We study the radial and azimuthal mass distribution of the lensing galaxy in WFI2033-4723. Mindful of the fact that modeling results depend on modeling assumptions, we examine two very different recent models: simply parametrized (SP) models from the H0LiCOW collaboration, and pixelated free-form (FF) GLASS models. In addition, we fit our own models which are a compromise between the astrophysical grounding of SP, and the flexibility of FF approaches. Our models consist of two offset parametric mass components, and generate many solutions, all fitting the quasar point image data. Among other results, we show that to reproduce point image properties the lensing mass must be lopsided, but the origin of this asymmetry can reside in the main lens plane or along the line of sight. We also show that there is a degeneracy between the slope of the density profile and the magnitude of external shear, and that the models from various modeling approaches are connected not by the mass sheet degeneracy, but by a more generalized transformation. Finally, we discuss interpretation degeneracy which afflicts all mass modeling: inability to correctly assign mass to the main lensing galaxy vs. nearby galaxies or line of sight structures. While this may not be a problem for the determination of $H_0$, interpretation degeneracy may become a major issue for the detailed study of galaxy structure.

Frequency and nature of central molecular outflows in nearby star-forming disk galaxies

Central molecular outflows in spiral galaxies are assumed to modulate their host galaxy’s star formation rate (SFR) by removing gas from the inner region of the galaxy. Outflows consisting of different gas phases appear to be a common feature in local galaxies, yet, little is known about the frequency of molecular outflows in main sequence galaxies in the nearby universe. We develop a rigorous set of selection criteria, which allow the reliable identification of outflows in large samples of galaxies. Our criteria make use of central spectra, position-velocity diagrams and velocity-integrated intensity maps (line-wing maps). We use this method on high-angular resolution CO (2–1) observations from the PHANGS-ALMA survey, which provides observations of the molecular gas for a homogeneous sample of 90 nearby main sequence galaxies at a resolution of ∼100 pc. We find correlations between the assigned outflow confidence and stellar mass or global SFR. We determine the frequency of central molecular outflows to be 25 ± 2% considering all outflow candidates, or 20 ± 2% for secure outflows only. Our resulting outflow candidate sample of 16−20 galaxies shows an overall enhanced fraction of active galactic nuclei (AGN) (50%) and bars (89%) compared to the full sample (galaxies with AGN: 24%, with bar: 61%). We extend the trend between mass outflow rates and SFR known for high outflow rates down to lower values (log10Ṁout[M⊙yr−1] < 0). Mass loading factors are of order unity, indicating that these outflows are not efficient in quenching the SFR in main sequence galaxies.

Two interacting galaxies hiding as one, revealed by MaNGA

Given their prominent role in galaxy evolution, it is of paramount importance to unveil galaxy interactions and merger events and to investigate the underlying mechanisms. The use of high-resolution data makes it easier to identify merging systems, but it can still be challenging when the morphology does not show any clear galaxy pair or gas bridge. Characterising the origin of puzzling kinematic features can help reveal complicated systems. Here, we present a merging galaxy, MaNGA 1-114955, in which we highlighted the superimposition of two distinct rotating discs along the line of sight. These counter-rotating objects both lie on the star-forming main sequence but display perturbed stellar velocity dispersions. The main galaxy presents off-centred star formation as well as off-centred high-metallicity regions, supporting the scenario of recent starbursts, while the secondary galaxy hosts a central starburst that coincides with an extended radio emission, in excess with respect to star formation expectations. Stellar mass as well as dynamical mass estimates agree towards a mass ratio within the visible radius of 9:1 for these interacting galaxies. We suggest that we are observing a pre-coalescence stage of a merger. The primary galaxy accreted gas through a past first pericentre passage about 1 Gyr ago and more recently from the secondary gas-rich galaxy, which exhibits an underlying active galactic nucleus. Our results demonstrate how a galaxy can hide another one and the relevance of a multi-component approach for studying ambiguous systems. We anticipate that our method will be efficient at unveiling the mechanisms taking place in a sub-sample of galaxies observed by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, all of which exhibit kinematic features of a puzzling origin in their gas emission lines.

Preparing for LSST data

Aims.We study how the upcoming Legacy Survey of Space and Time (LSST) data from theVera C. RubinObservatory can be employed to constrain the physical properties of normal star-forming galaxies (main-sequence galaxies). Because the majority of the observed LSST objects will have no auxiliary data, we use simulated LSST data and existing real observations to test the reliability of estimates of the physical properties of galaxies, such as their star formation rate (SFR), stellar mass (Mstar), and dust luminosity (Ldust). We focus on normal star-forming galaxies because they form the majority of the galaxy population in the universe and are therefore more likely to be observed with the LSST.Methods.We performed a simulation of LSST observations and uncertainties of 50 385 real galaxies within the redshift range 0 < z < 2.5. In order to achieve this goal, we used the unique multi-wavelength data from theHerschelExtragalactic Legacy Project (HELP) survey. Our analysis focused on two fields, ELAIS N1 and COSMOS. To obtain the physical properties of the galaxies, we fit their spectral energy distributions (SEDs) using the Code Investigating GALaxy Emission. We simulated the LSST data by convolving the SEDs fitted by employing the multi-wavelength observations. We compared the main galaxy physical properties, such as SFR,Mstar, andLdustobtained from the fit of the observed multi-wavelength photometry of galaxies (from the UV to the far-IR) to those obtained from the simulated LSST optical measurements alone.Results.We present the catalogue of simulated LSST observations for 23 291 main-sequence galaxies in the ELAIS N1 field and for 9093 galaxies in the COSMOS field. It is available in the HELP virtual observatory. The stellar masses estimated based on the LSST measurements agree with the full UV to far-IR SED estimates because they mainly depend on the UV and optical emission, which is well covered by LSST in the considered redshift range. Instead, we obtain a clear overestimate of the dust-related properties (SFR,Ldust,Mstar) estimated with the LSST alone. They are highly correlated with redshift. We investigate the cause of this overestimate and conclude that it is related to an overestimate of the dust attenuation in both UV and near-IR. We find that it is necessary to employ auxiliary rest-frame mid-IR observations, simulated UV observations, or the far-UV attenuation (AFUV)-Mstarrelation to correct for the overestimate. We also deliver the correction formula log10(SFRLSST/SFRreal) = 0.26 ⋅ z2 − 0.94 ⋅ z + 0.87. It is based on the 32 384 MS galaxies detected withHerschel.

Testing one-loop galaxy bias: Cosmological constraints from the power spectrum

We investigate the impact of different assumptions in the modeling of one-loop galaxy bias on the recovery of cosmological parameters, as a follow up of the analysis done in the first paper of the series at fixed cosmology. We use three different synthetic galaxy samples whose clustering properties match the ones of the CMASS and LOWZ catalogues of BOSS and the SDSS Main Galaxy Sample. We investigate the relevance of allowing for either short range non-locality or scale-dependent stochasticity by fitting the real-space galaxy auto power spectrum or the combination of galaxy-galaxy and galaxy-matter power spectrum. From a comparison among the goodness-of-fit ($\chi^2$), unbiasedness of cosmological parameters (FoB), and figure-of-merit (FoM), we find that a four-parameter model (linear, quadratic, cubic non-local bias, and constant shot-noise) with fixed quadratic tidal bias provides a robust modelling choice for the auto power spectrum of the three samples, up to $k_{\rm max}=0.3\,h\,\mathrm{Mpc}^{-1}$ and for an effective volume of $6\,h^{-3}\,\mathrm{Gpc}^3$. Instead, a joint analysis of the two observables fails at larger scales, and a model extension with either higher derivatives or scale-dependent shot-noise is necessary to reach a similar $k_{\rm max}$, with the latter providing the most stable results. These findings are obtained with three, either hybrid or perturbative, prescriptions for the matter power spectrum, \texttt{RESPRESSO}, gRPT and EFT. In all cases, the inclusion of scale-dependent shot-noise increases the range of validity of the model in terms of FoB and $\chi^2$. Interestingly, these model extensions with additional free parameters do not necessarily lead to an increase in the maximally achievable FoM for the cosmological parameters $\left(h,\,\Omega_ch^2,\,A_s\right)$, which are generally consistent to those of the simpler model at smaller $k_{\rm max}$.

The curious case of NGC 5068 and its neutral hydrogen fingers

AbstractHow galaxies replenish their gas supply in order to sustain star formation, is a research topic of many of the new and upcoming neutral atomic hydrogen (Hi) surveys on the SKA precursor instruments. This replenishment, or accretion, of gas in the form of Hi is likely to occur at column densities one or two orders of magnitude below previous observational limits and it has, so far, not been unambiguously detected. We present recent deep Hi observations of NGC 5068, an isolated nearby star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. This survey is the deepest Hi survey of nearby galaxies until the advent of the SKA and is reaching column densities of resolution. The combination of the resolution and sensitivity of the MeerKAT HI data have revealed “fingers” of low column density gas extending out from the main Hi disk of the galaxy. While the origin of these fingers remains a mystery for now, the dynamics of the main galaxy disk and the outer disk in which the fingers are located, as well as the morphology of the fingers, does not seem to suggest a previous merger event.

Giant star-forming complexes in high-z main-sequence galaxy analogues: the internal structure of clumps in DYNAMO galaxies

ABSTRACT To indirectly study the internal structure of giant clumps in main sequence galaxies at z ∼ 1–3, we target very turbulent and gas-rich local analogues from the DYNAMO sample with the Hubble Space Telescope, over a wavelength range of ∼200–480 nm. We present a catalogue of 58 clumps identified in six DYNAMO galaxies, including the WFC3/UVIS F225W, F336W, and F467M photometry where the (225–336) and (336–467) colours are sensitive to extinction and stellar population age, respectively. We measure the internal colour gradients of clumps themselves to study their age and extinction properties. We find a marked colour trend within individual clumps, where the resolved colour distributions show that clumps generally have bluer (336–467) colours (denoting very young ages) in their centres than at their edges, with little variation in the (225–336) colour associated with extinction. Furthermore, we find that clumps whose colours suggest they are older, are preferentially located closer towards the centres of their galaxies, and we find no young clumps at small galactocentric distances. Both results are consistent with simulations of high-redshift star-forming systems that show clumps form via violent disc instability, and through dynamic processes migrate to the centres of their galaxies to contribute to bulge growth on time-scales of a few 100 Myr, while continually forming stars in their centres. When we compare the DYNAMO clumps to those in these simulations, we find the best agreement with the long-lived clumps.

On the dark matter haloes of optical and IR-selected AGNs in the local universe

ABSTRACT We use the technique of total satellite luminosity, Lsat, to probe the dark matter haloes around active galactic nuclei (AGNs) in the SDSS Main Galaxy Sample. Our results focus on galaxies and AGNs that are the central galaxy of their halo. Our two AGN samples are constructed from optical emission-line diagnostics and from Wide-Field Infrared Survey Explorer (WISE) infrared colours. Both optically selected and WISE-selected AGN have Lsat values twice as high as non-active galaxy samples when controlling for stellar mass and mean stellar age. This implies that the haloes are twice as massive, but we cannot rule out that the increase in Lsat is due to these AGNs residing in younger haloes at the same mass. When only controlling for host galaxy stellar mass, WISE-selected AGNs also have higher Lsat values than optical AGNs at the factor of two level, consistent with previous results comparing the clustering of obscured and unobscured AGNs. However, controlling for stellar age in the two populations of host galaxies removes half of this difference, attenuating the statistical significance of the difference. We perform permutation tests to quantify the difference in the halo populations of each sample. The difference in star formation properties does not fully explain the difference in the two AGN populations, however. Although AGN luminosity correlates with mean stellar age, the difference in stellar age between the WISE and optical samples cannot be fully explained by differences in their AGN luminosity distributions.

One–Two Quench: A Double Minor Merger Scenario

Abstract Using the N-body+Smoothed particle hydrodynamics code, ChaNGa, we identify two merger-driven processes—disk disruption and supermassive black hole (SMBH) feedback—which work together to quench L * galaxies for over 7 Gyr. Specifically, we examine the cessation of star formation in a simulated Milky Way (MW) analog, driven by an interaction with two minor satellites. Both interactions occur within ∼100 Myr of each other, and the satellites both have masses 5–20 times smaller than that of their MW-like host galaxy. Using the genetic modification process of Roth et al., we generate a set of four zoom-in, MW-mass galaxies all of which exhibit unique star formation histories due to small changes to their assembly histories. In two of these four cases, the galaxy is quenched by z = 1. Because these are controlled modifications, we are able to isolate the effects of two closely spaced minor merger events, the relative timing of which determines whether the MW-mass main galaxy quenches. This one–two punch works to: (1) fuel the SMBH at its peak accretion rate and (2) disrupt the cold, gaseous disk of the host galaxy. The end result is that feedback from the SMBH thoroughly and abruptly ends the star formation of the galaxy by z ≈ 1. We search for and find a similar quenching event in Romulus25, a hydrodynamical (25 Mpc)3 volume simulation, demonstrating that the mechanism is common enough to occur even in a small sample of MW-mass quenched galaxies at z = 0.

The interstellar medium of quiescent galaxies and its evolution with time

We characterise the basic far-IR properties and the gas mass fraction of massive (⟨log(M*/M⊙)⟩ ≈ 11.0) quiescent galaxies (QGs) and explore how these evolve from z = 2.0 to the present day. We use robust, multi-wavelength (mid- to far-IR and sub-millimetre to radio) stacking ensembles of homogeneously selected and mass complete samples of log(M*/M⊙)≳10.8 QGs. We find that the dust to stellar mass ratio (Mdust/M*) rises steeply as a function of redshift up to z ∼ 1.0 and then remains flat at least out to z = 2.0. Using Mdust as a proxy of gas mass (Mgas), we find a similar trend for the evolution of the gas mass fraction (fgas), with z > 1.0 QGs having fgas ≈ 7.0% (for solar metallicity). This fgas is three to ten times lower than that of normal star-forming galaxies (SFGs) at their corresponding redshift but ≳3 and ≳10 times larger compared to that of z = 0.5 and local QGs. Furthermore, the inferred gas depletion time scales are comparable to those of local SFGs and systematically longer than those of main sequence galaxies at their corresponding redshifts. Our analysis also reveals that the average dust temperature (Td) of massive QGs remains roughly constant (⟨Td⟩ = 21.0 ± 2.0 K) at least out to z ≈ 2.0 and is substantially colder (ΔTd ≈ 10 K) compared to that of SFGs. This motivated us to construct and release a redshift-invariant template IR SED, that we used to make predictions for ALMA observations and to explore systematic effects in the Mgas estimates of massive, high-z QGs. Finally, we discuss how a simple model that considers progenitor bias can effectively reproduce the observed evolution of Mdust/M* and fgas. Our results indicate universal initial interstellar medium conditions for quenched galaxies and a large degree of uniformity in their internal processes across cosmic time.