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Register a new userPRIMUS+DEEP2: The Dependence of Galaxy Clustering on Stellar Mass and Specific Star Formation Rate at 0.2 < z < 1.2
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We present results on the clustering properties of galaxies as a function of both stellar mass and specific star formation rate (sSFR) using data from the PRIMUS and DEEP2 galaxy redshift surveys spanning 0.2 < z < 1.2. We use spectroscopic redshifts of over 100,000 galaxies covering an area of 7.2 deg^2 over five separate fields on the sky, from which we calculate cosmic variance errors. We find that the galaxy clustering amplitude is as strong of a function of sSFR as of stellar mass, and that at a given sSFR, it does not significantly depend on stellar mass within the range probed here. We further find that within the star-forming population and at a given stellar mass, galaxies above the main sequence of star formation with higher sSFR are less clustered than galaxies below the main sequence with lower sSFR. We also find that within the quiescent population, galaxies with higher sSFR are less clustered than galaxies with lower sSFR, at a given stellar mass. We show that the galaxy clustering amplitude smoothly increases with both increasing stellar mass and decreasing sSFR, implying that galaxies likely evolve across the main sequence, not only along it, before galaxies eventually become quiescent. These results imply that the stellar mass to halo mass relation, which connects galaxies to dark matter halos, likely depends on sSFR.
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We utilize $Lambda$CDM halo occupation models of galaxy clustering to investigate the evolving stellar mass dependent clustering of galaxies in the PRIsm MUlti-object Survey (PRIMUS) and DEEP2 Redshift Survey over the past eight billion years of cosmic time, between $0.2<z<1.2$. These clustering measurements provide new constraints on the connections between dark matter halo properties and galaxy properties in the context of the evolving large-scale structure of the universe. Using both an analytic model and a set of mock galaxy catalogs, we find a strong correlation between central galaxy stellar mass and dark matter halo mass over the range $M_mathrm{halo}sim10^{11}$-$10^{13}~h^{-1}M_odot$, approximately consistent with previous observations and theoretical predictions. However, the stellar-to-halo mass relation (SHMR) and the mass scale where star formation efficiency reaches a maximum appear to evolve more strongly than predicted by other models, including models based primarily on abundance-matching constraints. We find that the fraction of satellite galaxies in haloes of a given mass decreases significantly from $zsim0.5$ to $zsim0.9$, partly due to the fact that haloes at fixed mass are rarer at higher redshift and have lower abundances. We also find that the $M_1/M_mathrm{min}$ ratio, a model parameter that quantifies the critical mass above which haloes host at least one satellite, decreases from $approx20$ at $zsim0$ to $approx13$ at $zsim0.9$. Considering the evolution of the subhalo mass function vis-`{a}-vis satellite abundances, this trend has implications for relations between satellite galaxies and halo substructures and for intracluster mass, which we argue has grown due to stripped and disrupted satellites between $zsim0.9$ and $zsim0.5$.
We study the dependence of angular two-point correlation functions on stellar mass ($M_{*}$) and specific star formation rate (sSFR) of $M_{*}>10^{10}M_{odot}$ galaxies at $zsim1$. The data from UKIDSS DXS and CFHTLS covering 8.2 deg$^{2}$ sample scales larger than 100 $h^{-1}$Mpc at $zsim1$, allowing us to investigate the correlation between clustering, $M_{*}$, and star formation through halo modeling. Based on halo occupation distributions (HODs) of $M_{*}$ threshold samples, we derive HODs for $M_{*}$ binned galaxies, and then calculate the $M_{*}/M_{rm halo}$ ratio. The ratio for central galaxies shows a peak at $M_{rm halo}sim10^{12}h^{-1}M_{odot}$, and satellites predominantly contribute to the total stellar mass in cluster environments with $M_{*}/M_{rm halo}$ values of 0.01--0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies ($rm log,sSFR/yr^{-1}sim-9$) are mainly central galaxies in $sim10^{12.5} h^{-1}M_{odot}$ haloes with the lowest clustering amplitude, while lower sSFR galaxies consist of a mixture of both central and satellite galaxies where those with the lowest $M_{*}$ are predominantly satellites influenced by their environment. Considering the lowest $M_{rm halo}$ samples in each $M_{*}$ bin, massive central galaxies reside in more massive haloes with lower sSFRs than low mass ones, indicating star-forming central galaxies evolve from a low $M_{*}$--high sSFR to a high $M_{*}$--low sSFR regime. We also find that the most rapidly star-forming galaxies ($rm log,sSFR/yr^{-1}>-8.5$) are in more massive haloes than main sequence ones, possibly implying galaxy mergers in dense environments are driving the active star formation. These results support the conclusion that the majority of star-forming galaxies follow secular evolution through the sustained but decreasing formation of stars.
In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at $0.5<z<2.5$ selected from 3D-HST. We confirm that star-forming galaxies are larger than quiescent galaxies at fixed stellar mass (M$_{star}$). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27$pm$0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed M$_{star}$ takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/M$_{star}$, whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/M$_{star}$ at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of $>$0.5 dex in the central density threshold correlated with quiescence from $zsim0.7-2.0$. Neither a compact size nor high-$n$ are sufficient to assess the likelihood of quiescence for the average galaxy; rather, the combination of these two parameters together with M$_{star}$ results in a unique quenching threshold in central density/velocity.
We measure the clustering of X-ray, radio, and mid-IR-selected active galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7 separate fields spanning ~10 square degrees. Using the cross-correlation of AGN with dense galaxy samples, we measure the clustering scale length and slope, as well as the bias, of AGN selected at different wavelengths. Similar to previous studies, we find that X-ray and radio AGN are more clustered than mid-IR-selected AGN. We further compare the clustering of each AGN sample with matched galaxy samples designed to have the same stellar mass, star formation rate, and redshift distributions as the AGN host galaxies and find no significant differences between their clustering properties. The observed differences in the clustering of AGN selected at different wavelengths can therefore be explained by the clustering differences of their host populations, which have different distributions in both stellar mass and star formation rate. Selection biases inherent in AGN selection, therefore, determine the clustering of observed AGN samples. We further find no significant difference between the clustering of obscured and unobscured AGN, using IRAC or WISE colors or X-ray hardness ratio.
We use a robust sample of 11 z~7 galaxies (z-dropouts) to estimate the stellar mass density of the universe when it was only ~750 Myr old. We combine the very deep optical to near-Infrared photometry from the HST ACS and NICMOS cameras with mid-Infrared Spitzer IRAC imaging available through the GOODS program. After carefully removing the flux from contaminating foreground sources we have obtained reliable photometry in the 3.6 and 4.5 micron IRAC channels. The spectral shapes of these sources, including their rest frame optical colors, strongly support their being at z~7 with a mean photometric redshift of <z>=7.2+/-0.5. We use Bruzual & Charlot (2003) synthetic stellar population models to constrain their stellar masses and star formation histories. We find stellar masses that range over 0.1 -12x10^9 M_sol and average ages from 20 Myr to up to 425 Myr with a mean of ~300 Myr, suggesting that in some of these galaxies most of the stars were formed at z>8 (and probably at z>~10). The best fits to the observed SEDs are consistent with little or no dust extinction, in agreement with recent results at z~4-8. The star formation rates (SFR) are in the range from 5-20 M_sol/yr. From this sample we measure a stellar mass density of 6.6_{-3.3}^{+5.4}x10^5 M_sol/Mpc^3 to a limit of M_{UV,AB}<-20 (or 0.4 L*(z=3)). Combined with a fiducial lower limit for their ages (80 Myr) this implies a maximum SFR density of 0.008 M_sol/yr/Mpc^3. This is well below the critical level needed to reionize the universe at z~8 using standard assumptions. However, this result is based on luminous sources (>L*) and does not include the dominant contribution of the fainter galaxies. Strikingly, we find that the specific SFR is constant from z~7 to z~2 but drops substantially at more recent times.
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