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Galaxies' stellar masses, gas-phase oxygen abundances (metallicity), and star formation rates (SFRs) obey a series of empirical correlations, most notably the mass–metallicity relation (MZR) and fundamental metallicity relation (FZR), which relates oxygen abundance to a combination of stellar mass and SFR. However, due to the difficulty of measuring oxygen abundances and SFRs in galaxies that host powerful active galactic nuclei (AGN), to date it is unknown to what extent AGN-host galaxies also follow these correlations. In this work, we apply Bayesian methods to the MaNGA integral field spectrographic (IFS) survey that allow us to measure oxygen abundances and SFRs in AGN hosts, and use these measurements to explore how the MZR and FZR differ between galaxies that do and do not host AGN. We find similar MZRs at stellar masses above |$10^{10.5} \, \mathrm{M}_\odot$|⁠ , but that at lower stellar masses AGN hosts show up to |$\sim 0.2$|  dex higher oxygen abundances. The offset in the FZR is significantly smaller, suggesting that the larger deviation in the MZR is a result of AGN-host galaxies having systematically lower SFRs at fixed stellar mass. However, within the AGN-host sample there is little correlation between SFR and oxygen abundance. These findings support a scenario in which an AGN can halt efficient gas accretion, which drives non-AGN host galaxies to both higher SFR and lower oxygen abundance, resulting in the galaxy evolving off the star-forming main sequence (SFMS). As a consequence, as the SFR declines for an individual system its metallicity remains mostly unchanged. [ABSTRACT FROM AUTHOR]

The ALMaQUEST (ALMA-MaNGA QUEnching and STar formation) survey is a program with spatially resolved 12CO(1−0) measurements obtained with the Atacama Large Millimeter Array (ALMA) for 46 galaxies selected from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) DR15 optical integral-field spectroscopic survey. The aim of the ALMaQUEST survey is to investigate the dependence of star formation activity on the cold molecular gas content at kiloparsec scales in nearby galaxies. The sample consists of galaxies spanning a wide range in specific star formation rate (sSFR), including starburst (SB), main-sequence (MS), and green valley (GV) galaxies. In this paper, we present the sample selection and characteristics of the ALMA observations and showcase some of the key results enabled by the combination of spatially matched stellar populations and gas measurements. Considering the global (aperture-matched) stellar mass, molecular gas mass, and star formation rate of the sample, we find that the sSFR depends on both the star formation efficiency (SFE) and the molecular gas fraction (), although the correlation with the latter is slightly weaker. Furthermore, the dependence of sSFR on the molecular gas content (SFE or) is stronger than that on either the atomic gas fraction or the molecular-to-atomic gas fraction, albeit with the small H i sample size. On kiloparsec scales, the variations in both SFE and within individual galaxies can be as large as 1–2 dex, thereby demonstrating that the availability of spatially resolved observations is essential to understand the details of both star formation and quenching processes. [ABSTRACT FROM AUTHOR]

We present a multiwavelength study of the active galactic nucleus in the nearby (D = 14.1 Mpc) low-mass galaxy IC 750, which has circumnuclear 22 GHz water maser emission. The masers trace a nearly edge-on, warped disk ∼0.2 pc in diameter, coincident with the compact nuclear X-ray source that lies at the base of the ∼kiloparsec-scale extended X-ray emission. The position–velocity structure of the maser emission indicates that the central black hole (BH) has a mass less than 1.4 × 105 M⊙. Keplerian rotation curves fitted to these data yield enclosed masses between 4.1 × 104M⊙ and 1.4 × 105M⊙, with a mode of 7.2 × 104M⊙. Fitting the optical spectrum, we measure a nuclear stellar velocity dispersion km s−1. From near-infrared photometry, we fit a bulge mass of (7.3 ± 2.7) × 108M⊙ and a stellar mass of 1.4 × 1010M⊙. The mass upper limit of the intermediate-mass BH in IC 750 falls roughly two orders of magnitude below the MBH–σ* relation and roughly one order of magnitude below the MBH–MBulge and MBH–M* relations—larger than the relations' intrinsic scatters of 0.58 ± 0.09 dex, 0.69 dex, and 0.65 ± 0.09 dex, respectively. These offsets could be due to larger scatter at the low-mass end of these relations. Alternatively, BH growth is intrinsically inefficient in galaxies with low bulge and/or stellar masses, which causes the BHs to be undermassive relative to their hosts, as predicted by some galaxy evolution simulations. [ABSTRACT FROM AUTHOR]

Using long-slit spectroscopy from Moran et al. (2012), we constrain the radial dependence of the recent star formation histories of nearby galaxies with stellar masses greater than 1010 M⊙. By fitting stellar population models to the combination of specific star formation rate, Dn4000 and HγA, we show that the star formation histories of many disc galaxies cannot be accurately represented if their star formation rates declined exponentially with time. Many galaxies have Balmer absorption line equivalent widths that require recent short-lived episodes or bursts of star formation.The fraction of galaxies that have experienced episodic rather than continuous star formation is highest for ‘late-type’ galaxies with low stellar masses, low surface densities and low concentrations. In these systems, bursts occur both in the inner and in the outer regions of the galaxy. The fraction of stars formed in a single burst episode is typically around 15 per cent of the total stellar mass in the inner regions of the galaxy and around 5 per cent of the mass in the outer regions. When we average over the population, we find that such bursts contribute around a half of the total mass in stars formed in the last 2 Gyr. In massive galaxies, bursts occur predominantly in the outer disc. Around a third of all massive, bulge-dominated galaxies have experienced recent star formation episodes that are fully confined to their outer (R > 0.7R90) regions. The fraction of stars formed in bursts is only ∼2–3 per cent of the underlying stellar mass, but when we average over the population, we find that such bursts contribute nearly all the stellar mass formed in the last 2 Gyr.Recent star formation in outer discs is strongly correlated with the global atomic gas fraction of the galaxy, but not its global molecular gas fraction. We suggest that outer episodic star formation is triggered by gas accretion ‘events’. Episodic star formation in the inner regions is suppressed in galaxies with large bulge-to-disc ratio. This supports the idea that inner bursts are linked to instability-driven gas inflows. [ABSTRACT FROM AUTHOR]

ABSTRACT We use principal component analysis (PCA) to estimate stellar masses, mean stellar ages, star formation histories (SFHs), dust extinctions and stellar velocity dispersions for a set of ∼290 000 galaxies with stellar masses greater than 1011 M⊙ and redshifts in the range 0.4 < z < 0.7 from the Baryon Oscillation Spectroscopic Survey (BOSS). We find that the fraction of galaxies with active star formation first declines with increasing stellar mass, but then flattens above a stellar mass of 1011.5 M⊙ at z∼ 0.6. This is in striking contrast to z∼ 0.1, where the fraction of galaxies with active star formation declines monotonically with stellar mass. At stellar masses of 1012 M⊙, therefore, the evolution in the fraction of star-forming galaxies from z∼ 0.6 to the present day reaches a factor of ∼10. When we stack the spectra of the most massive, star-forming galaxies at z∼ 0.6, we find that half of their [O iii] emission is produced by active galactic nuclei. The black holes in these galaxies are accreting on average at ∼0.01 the Eddington rate. To obtain these results, we use the stellar population synthesis models of Bruzual & Charlot to generate a library of model spectra with a broad range of SFHs, metallicities, dust extinctions and stellar velocity dispersions. The PCA is run on this library to identify its principal components over the rest-frame wavelength range 3700-5500 Å. We demonstrate that linear combinations of these components can recover information equivalent to traditional spectral indices such as the 4000-Å break strength and Hδ A, with greatly improved signal-to-noise ratio (S/N). In addition, the method is able to recover physical parameters such as stellar mass-to-light ratio, mean stellar age, velocity dispersion and dust extinction from the relatively low S/N BOSS spectra. We examine in detail the sensitivity of our stellar mass estimates to the input parameters in our model library, showing that almost all changes result in systematic differences in log M* of 0.1 dex or less. The biggest differences are obtained when using different population synthesis models - stellar masses derived using Maraston et al. models are systematically smaller by up to 0.12 dex at young ages. [ABSTRACT FROM AUTHOR]

We study the redshift evolution of the dynamical properties of ∼180, 000 massive galaxies from SDSS-III/BOSS combined with a local early-type galaxy sample from SDSS-II in the redshift range 0.1 ⩽ z ⩽ 0.6. The typical stellar mass of this sample is M⋆ ∼2 × 1011M☼. We analyze the evolution of the galaxy parameters effective radius, stellar velocity dispersion, and the dynamical to stellar mass ratio with redshift. As the effective radii of BOSS galaxies at these redshifts are not well resolved in the Sloan Digital Sky Survey (SDSS) imaging we calibrate the SDSS size measurements with Hubble Space Telescope/COSMOS photometry for a sub-sample of galaxies. We further apply a correction for progenitor bias to build a sample which consists of a coeval, passively evolving population. Systematic errors due to size correction and the calculation of dynamical mass are assessed through Monte Carlo simulations. At fixed stellar or dynamical mass, we find moderate evolution in galaxy size and stellar velocity dispersion, in agreement with previous studies. We show that this results in a decrease of the dynamical to stellar mass ratio with redshift at >2σ significance. By combining our sample with high-redshift literature data, we find that this evolution of the dynamical to stellar mass ratio continues beyond z ∼ 0.7 up to z > 2 as Mdyn/M⋆ ∼(1 + z)–0.30 ± 0.12, further strengthening the evidence for an increase of Mdyn/M⋆ with cosmic time. This result is in line with recent predictions from galaxy formation simulations based on minor merger driven mass growth, in which the dark matter fraction within the half-light radius increases with cosmic time. [ABSTRACT FROM AUTHOR]