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Register a new userPhysical properties and environments of nearby galaxies
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We review the physical properties of nearby, relatively luminous galaxies, using results from newly available massive data sets together with more detailed observations. First, we present the global distribution of properties, including the optical and ultraviolet luminosity, stellar mass, and atomic gas mass functions. Second, we describe the shift of the galaxy population from late galaxy types in underdense regions to early galaxy types in overdense regions. We emphasize that the scaling relations followed by each galaxy type change very little with environment, with the exception of some minor but detectable effects. The shift in the population is apparent even at the densities of small groups and therefore cannot be exclusively due to physical processes operating in rich clusters. Third, we divide galaxies into four crude types -- spiral, lenticular, elliptical, and merging systems -- and describe some of their more detailed properties. We attempt to put these detailed properties into the global context provided by large surveys.
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The SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with $mu$Jy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact.
Mapping the molecular gas content of the universe is key to our understanding of the build-up of galaxies over cosmic time. Spectral line scans in deep fields, such as the Hubble Ultra Deep Field (HUDF), provide a unique view on the cold gas content out to high redshift. By conducting `spectroscopy-of-everything, these flux-limited observations are sensitive to the molecular gas in galaxies without preselection, revealing the cold gas content of galaxies that would not be selected in traditional studies. In order to capitalize on the molecular gas observations, knowledge about the physical conditions of the galaxies detected in molecular gas, such as their interstellar medium conditions, is key. Fortunately, deep surveys with integral-field spectrographs are providing an unprecedented view of the galaxy population, providing redshifts and measurements of restframe UV/optical lines for thousands of galaxies. We present the results from the synergy between the ALMA Spectroscopic Survey of the HUDF (ASPECS), with deep integral field spectroscopy from the MUSE HUDF survey and multi-wavelength data. We discuss the nature of the galaxies detected in molecular gas without preselection and their physical properties, such as star formation rate and metallicity. We show how the combination of ALMA and MUSE integral field spectroscopy can constrain the physical properties in galaxies located around the main sequence during the peak of galaxy formation.
We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive ($rm M_* sim 10^{11} M_{odot}$), compact starburst galaxies at z = 0.4-0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean $rm Sigma_{SFR} sim 3000 ,M_{odot} yr^{-1} kpc^{-2}$) and powerful galactic outflows (maximum speeds v$_{98} sim$ 1000-3000 km s$^{-1}$). Our unique data set includes an ensemble of both emission [OII]$lambdalambda$3726,3729, H$beta$, [OIII]$lambdalambda$4959,5007, H$alpha$, [NII]$lambdalambda$6548,6583, and [SII]$lambdalambda$6716,6731) and absorption MgII$lambdalambda$2796,2803, and FeII$lambda$2586) lines that allow us to investigate the kinematics of the cool gas phase (T$sim$10$^4$ K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (median n$_e sim$ 530 cm$^{-3}$), high metallicity (solar or super-solar), and, on average, high ionization parameters. We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [SII] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape.
The nearby Hydra Cluster ($sim$50 Mpc) is an ideal laboratory to understand, in detail, the influence of the environment on the morphology and quenching of galaxies in dense environments. We study the Hydra cluster galaxies in the inner regions ($1R_{200}$) of the cluster using data from the Southern Photometric Local Universe Survey (S-PLUS), which uses 12 narrow and broad band filters in the visible region of the spectrum. We analyse structural (Sersic index, effective radius) and physical (colours, stellar masses and star formation rates) properties. Based on this analysis, we find that $sim$88 percent of the Hydra cluster galaxies are quenched. Using the Dressler-Schectman test approach, we also find that the cluster shows possible substructures. Our analysis of the phase-space diagram together with DBSCAN algorithm indicates that Hydra shows an additional substructure that appears to be in front of the cluster centre, which is still falling into it. Our results, thus, suggest that the Hydra Cluster might not be relaxed. We analyse the median Sersic index as a function of wavelength and find that for red ($(u-r)geq$2.3) and early-type galaxies it displays a slight increase towards redder filters (13 and 18 percent, for red and early-type respectively) whereas for blue+green ($(u-r)$<2.3) galaxies it remains constant. Late-type galaxies show a small decrease of the median Sersic index toward redder filters. Also, the Sersic index of galaxies, and thus their structural properties, do not significantly vary as a function of clustercentric distance and density within the cluster; and this is the case regardless of the filter.
We present an enhanced version of the multiwavelength spectral modeling code MAGPHYS that allows the estimation of galaxy photometric redshift and physical properties (e.g., stellar mass, star formation rate, dust attenuation) simultaneously, together with robust characterization of their uncertainties. The self-consistent modeling over ultraviolet to radio wavelengths in MAGPHYS+photo-z is unique compared to standard photometric redshift codes. The broader wavelength consideration is particularly useful for breaking certain degeneracies in color vs. redshift for dusty galaxies with limited observer-frame ultraviolet and optical data (or upper limits). We demonstrate the success of the code in estimating redshifts and physical properties for over 4,000 infrared-detected galaxies at 0.4<z<6.0 in the COSMOS field with robust spectroscopic redshifts. We achieve high photo-z precision ($sigma_{Delta z/(1+z_{spec})}lesssim0.04$), high accuracy (i.e., minimal offset biases; median$(Delta z/(1+z_{spec}))lesssim0.02$), and low catastrophic failure rates ($etasimeq4%$) over all redshifts. Interestingly, we find that a weak 2175A absorption feature in the attenuation curve models is required to remove a subtle systematic photo-z offset ($z_{phot}-z_{spec}simeq-0.03$) that occurs when this feature is not included. As expected, the accuracy of derived physical properties in MAGPHYS+photo-z decreases strongly as redshift uncertainty increases. The all-in-one treatment of uncertainties afforded with this code is beneficial for accurately interpreting physical properties of galaxies in large photometric datasets. Finally, we emphasize that MAGPHYS+photo-z is not intended to replace existing photo-z codes, but rather offer flexibility to robustly interpret physical properties when spectroscopic redshifts are unavailable. The MAGPHYS+photo-z code is publicly available online.
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