Weighted correlation functions are an increasingly important tool for understanding how galaxy properties depend on their separation from each other. We use a mock galaxy sample drawn from the ...Millenium simulation, assigning weights using a simple prescription to illustrate and explore how well a weighted correlation function recovers the true radial dependence of the input weights. We find that the use of a weighted correlation function results in a dilution of the magnitude of any radial dependence of properties and a smearing out of that radial dependence in radius, compared to the input behavior. We present a quantitative discussion of the dilution in the magnitude of radial dependence in properties in the special case of a constant enhancement at r < rc. In this particular case where there was a SFR enhancement at small radius r < rc = 35 kpc, the matching of one member of an enhanced pair with a non-enhanced galaxy in the same group gives an artificial enhancement out to large radius ~ 200 kpc. We compare this with observations of SFR enhancement from the SDSS (Li et al. 2008; MNRAS, 385, 1903) finding very similar behavior - a significant enhancement at radii < 40 kpc and a weak enhancement out to more than 150 kpc. While we explore a particular case in this Letter, it is easy to see that the phenomenon is general, and precision analyses of weighted correlation functions will need to account carefully for this effect using simulated mock catalogs.
We present synthetic far- and near-ultraviolet (FUV and NUV) maps of M31, both with and without dust reddening. These maps were constructed from spatially-resolved star formation histories (SFHs) ...derived from optical Hubble Space Telescope imaging of resolved stars, taken as part of the Panchromatic Hubble Andromeda Treasury program. We use stellar population synthesis modeling to generate synthetic UV maps with projected spatial resolution of \(\sim\)100 pc (\(\sim\)24 arcseconds) The predicted UV flux agrees well with the observed flux, with median ratios between the modeled and observed flux of \(\log_{10}(f^{syn}/f^{obs}) = 0.03\pm0.24\) and \(-0.03\pm0.16\) in the FUV and NUV, respectively. This agreement is particularly impressive given that we used only optical photometry to construct these UV maps. We use the dust-free maps to examine properties of obscured flux and star formation by comparing our reddened and dust-free FUV flux maps with the observed FUV and FUV+24{\mu}m flux to examine the fraction of obscured flux. The synthetic flux maps require that \(\sim\)90% of the FUV flux in M31 is obscured by dust, while the GALEX-based methods suggest that \(\sim\)70% of the flux is obscured. This increase in the obscured flux estimate is driven by significant differences between the dust-free synthetic FUV flux and that derived when correcting the observed FUV for dust with 24{\mu}m observations. The difference is further illustrated when we compare the SFRs derived from the FUV+24{\mu}m flux with the 100 Myr average SFR from the SFHs. The 24{\mu}m-corrected FUV flux underestimates the SFR by a factor of \(\sim\)2.3 - 2.5. abridged
We present the second data release of the Large Early Galaxy Astrophysics Census (LEGA-C), an ESO 130-night public spectroscopic survey conducted with VIMOS on the Very Large Telescope. We release ...1988 spectra with typical continuum S / N ~= 20 /Angstrom of galaxies at 0.6 ~< z ~< 1.0, each observed for ~20 hours and fully reduced with a custom-built pipeline. We also release a catalog with spectroscopic redshifts, emission line fluxes, Lick/IDS indices, and observed stellar and gas velocity dispersions that are spatially integrated quantities including both rotational motions and genuine dispersion. To illustrate the new parameter space in the intermediate redshift regime probed by LEGA-C we explore relationships between dynamical and stellar population properties. The star-forming galaxies typically have observed stellar velocity dispersions of ~150 km/s and strong Hdelta absorption (Hd_A ~ 5 Angstrom), while passive galaxies have higher observed stellar velocity dispersions ~200 km/s and weak Hdelta absortion (Hd_A ~ 0 Angstrom). Strong O III5007 / Hbeta ratios tend to occur mostly for galaxies with weak Hd_A or galaxies with higher observed velocity dispersion. Beyond these broad trends, we find a large diversity of possible combinations of rest-frame colors, absorption line strengths and emission line detections, illustrating the utility of spectroscopic measurements to more accurately understand galaxy evolution. By making the spectra and value-added catalogs publicly available we encourage the community to take advantage of this very substantial investment in telescope time provided by ESO.
We explore the connection between the kinematics, structures and stellar populations of massive galaxies at \(0.6<z<1.0\) using the Fundamental Plane (FP). Combining stellar kinematic data from the ...Large Early Galaxy Astrophysics Census (LEGA-C) survey with structural parameters measured from deep Hubble Space Telescope imaging, we obtain a sample of 1419 massive (\(\log(M_*/M_\odot) >10.5\)) galaxies that span a wide range in morphology, star formation activity and environment, and therefore is representative of the massive galaxy population at \(z\sim0.8\). We find that quiescent and star-forming galaxies occupy the parameter space of the \(g\)-band FP differently and thus have different distributions in the dynamical mass-to-light ratio (\(M_{\rm dyn}/L_g\)), largely owing to differences in the stellar age and recent star formation history, and, to a lesser extent, the effects of dust attenuation. In contrast, we show that both star-forming and quiescent galaxies lie on the same mass FP at \(z\sim 0.8\), with a comparable level of intrinsic scatter about the plane. We examine the variation in \(M_{\rm dyn}/M_*\) through the thickness of the mass FP, finding no significant residual correlations with stellar population properties, Sérsic index, or galaxy overdensity. Our results suggest that, at fixed size and velocity dispersion, the variations in \(M_{\rm dyn}/L_g\) of massive galaxies reflect an approximately equal contribution of variations in \(M_*/L_g\), and variations in the dark matter fraction or initial mass function.
We report the discovery of a new dwarf galaxy, Andromeda XXIX, using data from the recently-released Sloan Digital Sky Survey DR8, and confirmed by Gemini North telescope Multi-Object Spectrograph ...imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15 degrees from M31, with a distance inferred from the tip of the red giant branch of 730kpc+/-75kpc, corresponding to a three dimensional separation from M31 of between 205kpc and 227kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, is M_V = -8.3+/-0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of Fe/H\sim-1.8. The half-light radius of And XXIX is 360pc+/-60pc and its ellipticity is 0.35+/-0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.
We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently-released SDSS DR8. The galaxy is a likely satellite of Andromeda, and, at a separation of ...\(365^{+17}_{-1}\) kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is \(650^{+150}_{-80}\) kpc, and analysis of its structure and luminosity show that it has an absolute magnitude of \(M_V = -8.5^{+0.4}_{-1.0}\) and half-light radius of \(r_h = 210^{+60}_{-50}\) pc, similar to many other faint Local Group dwarfs. With presently-available imaging we are unable to determine if there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or dwarf irregular.
We use the semi-analytic model developed by Henriques et al. (2015) to explore the origin of star formation history diversity for galaxies that lie at the centre of their dark matter haloes and have ...present-day stellar masses in the range 5-8 \(\times\) 10\(^{10}\) M\(_{\odot}\), similar to that of the Milky Way. In this model, quenching is the dominant physical mechanism for introducing scatter in the growth histories of these galaxies. We find that present-day quiescent galaxies have a larger variety of growth histories than star-formers since they underwent 'staggered quenching' - a term describing the correlation between the time of quenching and present-day halo mass. While halo mass correlates broadly with quiescence, we find that quiescence is primarily a function of black hole mass, where galaxies quench when heating from their active galactic nuclei becomes sufficient to offset the redshift-dependent cooling rate. In this model, the emergence of a prominent quiescent population is the main process that flattens the stellar mass-halo mass relation at mass scales at or above that of the Milky Way.
The DESI Legacy Imaging Surveys are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will ...jointly image approximately 14,000 deg^2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12 and 22 micorons) observed by the Wide-field Infrared Survey Explorer (WISE) satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project.
Drawing from the LEGA-C dataset, we present the spectroscopic view of the
stellar population across a large volume- and mass-selected sample of galaxies
at large lookback time. We measure the ...4000\AA\ break (D$_n$4000) and Balmer
absorption line strengths (probed by H$\delta$) from 1019 high-quality spectra
of $z=0.6 - 1.0$ galaxies with $M_\ast = 2 \times 10^{10} M_\odot - 3 \times
10^{11} M_\odot$. Our analysis serves as a first illustration of the power of
high-resolution, high-S/N continuum spectroscopy at intermediate redshifts as a
qualitatively new tool to constrain galaxy formation models. The observed
D$_n$4000-EW(H$\delta$) distribution of our sample overlaps with the
distribution traced by present-day galaxies, but $z\sim 0.8$ galaxies populate
that locus in a fundamentally different manner. While old galaxies dominate the
present-day population at all stellar masses $> 2\times10^{10} M_\odot$, we see
a bimodal D$_n$4000-EW(H$\delta$) distribution at $z\sim0.8$, implying a
bimodal light-weighted age distribution. The light-weighted age depends
strongly on stellar mass, with the most massive galaxies
$>1\times10^{11}M_\odot$ being almost all older than 2 Gyr. At the same time we
estimate that galaxies in this high mass range are only $\sim3$ Gyr younger
than their $z\sim0.1$ counterparts, at odd with pure passive evolution given a
difference in lookback time of $>5$ Gyr; younger galaxies must grow to
$>10^{11}M_\odot$ in the meantime, and/or small amounts of young stars must
keep the light-weighted ages young. Star-forming galaxies at $z\sim0.8$ have
stronger H$\delta$ absorption than present-day galaxies with the same
D$_n$4000, implying larger short-term variations in star-formation activity.
We report on the discovery of two low-luminosity, broad-line AGN at \(z>5\) identified using JWST NIRSpec spectroscopy from the CEERS Survey. We detect broad H\(\alpha\) emission from both sources, ...with FWHM of \(2038\pm286\) and \(1807\pm207\) km s\(^{-1}\), resulting in black hole (BH) masses that are 1-2 dex below that of existing samples of luminous quasars at \(z>5\). The first source, CEERS 1670 at \(z=5.242\), is 2-3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity AGN based on its rest-frame optical SED. We measure a BH mass of \(M_{\rm BH}=1.3\pm0.4\times 10^{7}~M_{\odot}\), confirming that this AGN is powered by the least-massive BH known in the universe at the end of cosmic reionization. The second source, CEERS 3210 at \(z=5.624\), is inferred to be a heavily obscured, broad-line AGN caught in a transition phase between a dust-obscured starburst and an unobscured quasar. We estimate its BH mass to be \(M_{\rm BH}\simeq 0.9-4.7 \times 10^{7}~M_{\odot}\), depending on the level of dust obscuration assumed. We derive host stellar masses, \(M_\star\), allowing us to place constraints on the BH-galaxy mass relationship in the lowest mass range yet probed in the early universe. The \(M_{\rm BH}/M_\star\) ratio for CEERS 1670, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at \(z=0\). We examine the emission-line ratios of both sources and find that their location on the BPT and OHNO diagrams is consistent with model predictions for low-metallicity AGN with \(Z/Z_\odot \simeq 0.2-0.4\). The spectroscopic identification of low-luminosity, broad-line AGN at \(z>5\) with \(M_{\rm BH}\simeq 10^{7}~M_{\odot}\) demonstrates the capability of JWST to push BH masses closer to the range predicted for the BH seed population and provides a unique opportunity to study the early stages of BH-galaxy assembly.
