The SAMI Galaxy Survey: Revising the Fraction of Slow Rotators in IFS Galaxy Surveys

The fraction of galaxies supported by internal rotation compared to galaxies stabilized by internal pressure provides a strong constraint on galaxy formation models. In integral field spectroscopy surveys, this fraction is biased because survey instruments typically only trace the inner parts of the most massive galaxies. We present aperture corrections for the two most widely used stellar kinematic quantities $V/\sigma$ and $\lambda_{R}$. Our demonstration involves integral field data from the SAMI Galaxy Survey and the ATLAS$^{\rm{3D}}$ Survey. We find a tight relation for both $V/\sigma$ and $\lambda_{R}$ when measured in different apertures that can be used as a linear transformation as a function of radius, i.e., a first-order aperture correction. We find that $V/\sigma$ and $\lambda_{R}$ radial growth curves are well approximated by second order polynomials. By only fitting the inner profile (0.5$R_{\rm{e}}$), we successfully recover the profile out to one $R_{\rm{e}}$ if a constraint between the linear and quadratic parameter in the fit is applied. However, the aperture corrections for $V/\sigma$ and $\lambda_{R}$ derived by extrapolating the profiles perform as well as applying a first-order correction. With our aperture-corrected $\lambda_{R}$ measurements, we find that the fraction of slow rotating galaxies increases with stellar mass. For galaxies with $\log M_{*}/M_{\odot}>$ 11, the fraction of slow rotators is $35.9\pm4.3$ percent, but is underestimated if galaxies without coverage beyond one $R_{\rm{e}}$ are not included in the sample ($24.2\pm5.3$ percent). With measurements out to the largest aperture radius the slow rotator fraction is similar as compared to using aperture corrected values ($38.3\pm4.4$ percent). Thus, aperture effects can significantly bias stellar kinematic IFS studies, but this bias can now be removed with the method outlined here.Comment: Accepted for Publication in the Monthly Notices of the Royal Astronomical Society. 16 pages and 11 figures. The key figures of the paper are: 1, 4, 9, and 1

The SAMI Galaxy Survey: mass-kinematics scaling relations

We use data from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) Galaxy Survey to study the dynamical scaling relation between galaxy stellar mass $M_*$ and the general kinematic parameter $S_K = \sqrt{K V_{rot}^2 + \sigma^2}$ that combines rotation velocity $V_{rot}$ and velocity dispersion $\sigma$. We show that the $\log M_* - \log S_K$ relation: (1)~is linear above limits set by properties of the samples and observations; (2)~has slightly different slope when derived from stellar or gas kinematic measurements; (3)~applies to both early-type and late-type galaxies and has smaller scatter than either the Tully-Fisher relation ($\log M_* - \log V_{rot}$) for late types or the Faber-Jackson relation ($\log M_* - \log\sigma$) for early types; and (4)~has scatter that is only weakly sensitive to the value of $K$, with minimum scatter for $K$ in the range 0.4 and 0.7. We compare $S_K$ to the aperture second moment (the `aperture velocity dispersion') measured from the integrated spectrum within a 3-arcsecond radius aperture ($\sigma_{3^{\prime\prime}}$). We find that while $S_{K}$ and $\sigma_{3^{\prime\prime}}$ are in general tightly correlated, the $\log M_* - \log S_K$ relation has less scatter than the $\log M_* - \log \sigma_{3^{\prime\prime}}$ relation.Comment: 14 pages, 8 figures, Accepted 2019 May 22. Received 2019 May 18; in original form 2019 January

A Pair of Compact Red Galaxies at Redshift 2.38, Immersed in a 100 kpc Scale Ly-alpha Nebula

We present Hubble Space Telescope (HST) and ground-based observations of a pair of galaxies at redshift 2.38, which are collectively known as 2142-4420 B1 (Francis et al. 1996). The two galaxies are both luminous extremely red objects (EROs), separated by 0.8 arcsec. They are embedded within a 100 kpc scale diffuse Ly-alpha nebula (or blob) of luminosity ~10^44 erg/s. The radial profiles and colors of both red objects are most naturally explained if they are young elliptical galaxies: the most distant yet found. It is not, however, possible to rule out a model in which they are abnormally compact, extremely dusty starbursting disk galaxies. If they are elliptical galaxies, their stellar populations have inferred masses of ~10^11 solar masses and ages of ~7x10^8 years. Both galaxies have color gradients: their centers are significantly bluer than their outer regions. The surface brightness of both galaxies is roughly an order of magnitude greater than would be predicted by the Kormendy relation. A chain of diffuse star formation extending 1 arcsec from the galaxies may be evidence that they are interacting or merging. The Ly-alpha nebula surrounding the galaxies shows apparent velocity substructure of amplitude ~ 700 km/s. We propose that the Ly-alpha emission from this nebula may be produced by fast shocks, powered either by a galactic superwind or by the release of gravitational potential energy.Comment: 33 pages, 9 figures, ApJ in press (to appear in Jun 10 issue

The SAMI Galaxy Survey: gravitational potential and surface density drive stellar populations -- I. early-type galaxies

The well-established correlations between the mass of a galaxy and the properties of its stars are considered evidence for mass driving the evolution of the stellar population. However, for early-type galaxies (ETGs), we find that $g-i$ color and stellar metallicity [Z/H] correlate more strongly with gravitational potential $\Phi$ than with mass $M$, whereas stellar population age correlates best with surface density $\Sigma$. Specifically, for our sample of 625 ETGs with integral-field spectroscopy from the SAMI Galaxy Survey, compared to correlations with mass, the color--$\Phi$, [Z/H]--$\Phi$, and age--$\Sigma$ relations show both smaller scatter and less residual trend with galaxy size. For the star formation duration proxy [$\alpha$/Fe], we find comparable results for trends with $\Phi$ and $\Sigma$, with both being significantly stronger than the [$\alpha$/Fe]-$M$ relation. In determining the strength of a trend, we analyze both the overall scatter, and the observational uncertainty on the parameters, in order to compare the intrinsic scatter in each correlation. These results lead us to the following inferences and interpretations: (1) the color--$\Phi$ diagram is a more precise tool for determining the developmental stage of the stellar population than the conventional color--mass diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity. Furthermore, we propose the following two mechanisms for the age and [$\alpha$/Fe] relations with $\Sigma$: (a) the age--$\Sigma$ and [$\alpha$/Fe]--$\Sigma$ correlations arise as results of compactness driven quenching mechanisms; and/or (b) as fossil records of the $\Sigma_{SFR}\propto\Sigma_{gas}$ relation in their disk-dominated progenitors.Comment: 9 pages, 4 figures, 1 table Accepted to Ap

The SAMI Galaxy Survey: Global stellar populations on the size-mass plane

We present an analysis of the global stellar populations of galaxies in the SAMI Galaxy Survey. Our sample consists of 1319 galaxies spanning four orders of magnitude in stellar mass and includes all morphologies and environments. We derive luminosity-weighted, single stellar population equivalent stellar ages, metallicities and alpha enhancements from spectra integrated within one effective radius apertures. Variations in galaxy size explain the majority of the scatter in the age--mass and metallicity--mass relations. Stellar populations vary systematically in the plane of galaxy size and stellar mass, such that galaxies with high stellar surface mass density are older, more metal-rich and alpha-enhanced than less dense galaxies. Galaxies with high surface mass densities have a very narrow range of metallicities, however, at fixed mass, the spread in metallicity increases substantially with increasing galaxy size (decreasing density). We identify residual correlations with morphology and environment. At fixed mass and size, galaxies with late-type morphologies, small bulges and low Sersic n are younger than early-type, high n, high bulge-to-total galaxies. Age and metallicity both show small residual correlations with environment; at fixed mass and size, galaxies in denser environments or more massive halos are older and somewhat more metal rich than those in less dense environments. We connect these trends to evolutionary tracks within the size--mass plane.Comment: 25 pages, 18 figures, MNRAS in press Corrected typo in author lis

The 2dF Galaxy Redshift Survey: power-spectrum analysis of the final data set and cosmological implications

We present a power-spectrum analysis of the final 2dF Galaxy Redshift Survey (2dFGRS), employing a direct Fourier method. The sample used comprises 221 414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection, improving on previous treatments in a number of respects. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys, which are used to demonstrate that the input cosmological model can be correctly recovered. We discuss in detail the possible differences between the galaxy and mass power spectra, and treat these using simulations, analytic models and a hybrid empirical approach. Based on these investigations, we are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the ‘baryon oscillations' that are predicted in cold dark matter (CDM) models. Fitting to a CDM model, assuming a primordial ns= 1 spectrum, h= 0.72 and negligible neutrino mass, the preferred parameters are Ωmh= 0.168 ± 0.016 and a baryon fraction Ωb/Ωm= 0.185 ± 0.046 (1σ errors). The value of Ωmh is 1σ lower than the 0.20 ± 0.03 in our 2001 analysis of the partially complete 2dFGRS. This shift is largely due to the signal from the newly sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard Ωm= 0.3: in combination with cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP), we infer Ωm= 0.231 ± 0.02

Galaxy and Mass Assembly: FUV, NUV, ugrizYJHK Petrosian, Kron and Sérsic photometry

In order to generate credible 0.1-2 μm spectral energy distributions, the Galaxy and Mass Assembly (GAMA) project requires many gigabytes of imaging data from a number of instruments to be reprocessed into a standard format. In this paper, we discuss the software infrastructure we use, and create self-consistent ugrizYJHK photometry for all sources within the GAMA sample. Using UKIDSS and SDSS archive data, we outline the pre-processing necessary to standardize all images to a common zero-point, the steps taken to correct for the seeing bias across the data set and the creation of gigapixel-scale mosaics of the three 4 × 12 deg2 GAMA regions in each filter. From these mosaics, we extract source catalogues for the GAMA regions using elliptical Kron and Petrosian matched apertures. We also calculate Sérsic magnitudes for all galaxies within the GAMA sample using sigma, a galaxy component modelling wrapper for galfit 3. We compare the resultant photometry directly and also calculate the r-band galaxy luminosity function for all photometric data sets to highlight the uncertainty introduced by the photometric method. We find that (1) changing the object detection threshold has a minor effect on the best-fitting Schechter parameters of the overall population (M*± 0.055 mag, α± 0.014, ϕ*± 0.0005 h3 Mpc−3); (2) there is an offset between data sets that use Kron or Petrosian photometry, regardless of the filter; (3) the decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag; (4) the best-fitting Schechter parameters from total-magnitude photometric systems (such as SDSS modelmag or Sérsic magnitudes) have a steeper faint-end slope than photometric systems based upon Kron or Petrosian measurements; and (5) our Universe's total luminosity density, when calculated using Kron or Petrosian r-band photometry, is underestimated by at least 15 per cen