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Register a new userThe MUSE Extremely Deep Field: Evidence for SFR-induced cores in dark-matter dominated galaxies at z=1
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Disc-halo decomposition on rotationally supported star-forming galaxies (SFGs) at $z>1$ are often limited to massive galaxies ($M_star>10^{10}~M_odot$) and rely on either deep Integral Field Spectroscopy data or stacking analyses. We present a study of the dark matter (DM) content of 9 $zapprox1$ SFGs selected Using the brightest [OII] emitters in the deepest Multi-Unit Spectrograph Explorer (MUSE) field to date, namely the 140hr MUSE Extremely Deep Field, we perform disk-halo decompositions on 9 low-mass SFGs (with $10^{8.5}<M_star<10^{10.5}~M_odot$) using a novel 3D modeling approach, which together with the exquisite S/N allows us to measure individual rotation curves to $3times R_e$. The DM component primarily uses the generalized $alpha,beta,gamma$ profile from Di Cintio et al., or a Navarro-Frenk-White (NFW) profile. The disk stellar masses $M_star$ obtained from the [OII] disk-halo decomposition agree with the values inferred from the spectral energy distributions. While the rotation curves show diverse shapes, ranging from rising to declining at large radii, the DM fractions within the half-light radius $f_{rm DM}(<R_e)$ are found to be 60% to 95%, extending to lower masses (densities) the results of Genzel et al., who found low DM fractions in SFGs with $M_star>10^{10}~M_odot$. The DM halos show constant surface densities of $sim100~M_odot$ pc$^{-2}$. Half of the sample shows a strong preference for cored over cuspy DM profiles. The presence of DM cores appears to be related to galaxies with stellar-to-halo mass $log M_star/M_{rm vir}approx-2.5$. In addition, the cuspiness of the DM profiles is found to be a strong function of the recent star-formation activity. Both of these results are interpreted as evidence for feedback-induced core formation in the Cold Dark Matter context.
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Recent large surveys have found a reversal of the star formation rate (SFR)-density relation at z=1 from that at z=0 (e.g. Elbaz et al.; Cooper et al.), while the sign of the slope of the color-density relation remains unchanged (e.g. Cucciati et al.; Quadri et al.). We use state-of-the-art adaptive mesh refinement cosmological hydrodynamic simulations of a 21x24x20 (Mpc/h)$^3$ region centered on a cluster to examine the SFR-density and color-density relations of galaxies at z=0 and z=1. The local environmental density is defined by the dark matter mass in spheres of radius 1 Mpc/h, and we probe two decades of environmental densities. Our simulations produce a large increase of SFR with density at z=1, as in the observations of Elbaz et al. We also find a significant evolution to z=0, where the SFR-density relation is much flatter. The color-density relation in our simulations is consistent from z=1 to z=0, in agreement with observations. We find that the increase in the median SFR with local density at z=1 is due to a growing population of star-forming galaxies in higher-density environments. At z=0 and z=1 both the SFR and cold gas mass are tightly correlated with the galaxy halo mass, and therefore the correlation between median halo mass and local density is an important cause of the SFR-density relation at both redshifts. We also show that the local density on 1 Mpc/h scales affects galaxy SFRs as much as halo mass at z=0. Finally, we find indications that the role of the 1 Mpc/h scale environment reverses from z=0 to z=1: at z=0 high-density environments depress galaxy SFRs, while at z=1 high-density environments tend to increase SFRs.
We present a observational study of the dark matter fraction in 225 rotation supported star-forming galaxies at $zapprox 0.9$ having stellar mass range: $ 9.0 leq log(M_* mathrm{M_odot}) leq 11.0$ and star formation rate: $0.49 leq log left(SFR mathrm{[M_{odot} yr^{-1}]} right) leq 1.77$. This is a sub sample of KMOS redshift one spectroscopic survey (KROSS) previously studied by citet{GS20}. The stellar masses ($M_*$) of these objects were previously estimated using mass-to-light ratios derived from fitting the spectral energy distribution of the galaxies. Star formation rates were derived from the H$_alpha$ luminosities. The total gas masses ($M_{gas}$) are determined by scaling relations of molecular and atomic gas citep[][respectively] {Tacconi2018, Lagos2011}. The dynamical masses ($M_{dyn}$) are directly derived from the rotation curves (RCs) at different scale lengths (effective radius: $R_e$, $sim 2 R_e$ and $sim 3 R_e$) and then the dark matter fractions ($f_{ DM }=1-M_{bar}/M_{dyn}$) at these radii are calculated. We report that at $zsim 1$ only a small fraction ($sim 5%$) of our sample has a low ($< 20%$) DM fraction within $sim$ 2-3 $R_e$. The majority ($> 72%$) of SFGs in our sample have dark matter dominated outer disks ($sim 5-10$ kpc) in agreement with local SFGs. Moreover, we find a large scatter in the fraction of dark matter at a given stellar mass (or circular velocity) with respect to local SFGs, suggesting that galaxies at $z sim 1$, a) span a wide range of stages in the formation of stellar disks, b) have diverse DM halo properties coupled with baryons.
In the standard cosmological model, dark matter drives the structure formation and constructs potential wells within which galaxies may form. The baryon fraction in dark halos can reach the universal value (15.7%) in massive clusters and decreases rapidly as the mass of the system decreases. The formation of dwarf galaxies is sensitive both to baryonic processes and the properties of dark matter owing to the shallow potential wells in which they form. In dwarf galaxies in the Local Group, dark matter dominates the mass content even within their optical-light half-radii (r_e ~ 1 kpc). However, recently it has been argued that not all dwarf galaxies are dominated by dark matter. Here we report 19 dwarf galaxies that could consist mainly of baryons up to radii well beyond r_e, at which point they are expected to be dominated by dark matter. Of these, 14 are isolated dwarf galaxies, free from the influence of nearby bright galaxies and high dense environments. This result provides observational evidence that could challenge the formation theory of low-mass galaxies within the framework of standard cosmology. Further observations, in particular deep imaging and spatially-resolved kinematics, are needed to constrain the baryon fraction better in such galaxies.
We report the discovery of diffuse extended Ly-alpha emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5-4 comoving Mpc. These structures have been observed in overdensities of Ly-alpha emitters in the MUSE Extremely Deep Field, a 140 hour deep MUSE observation located in the Hubble Ultra Deep Field. Among the 22 overdense regions identified, 5 are likely to harbor very extended Ly-alpha emission at high significance with an average surface brightness of $mathrm{5 times 10^{-20} erg s^{-1} cm^{-2} arcsec^{-2}}$. Remarkably, 70% of the total Ly-alpha luminosity from these filaments comes from beyond the circumgalactic medium of any identified Ly-alpha emitters. Fluorescent Ly-alpha emission powered by the cosmic UV background can only account for less than 34% of this emission at z$approx$3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Ly-alpha emission of a large population of ultra low luminosity Ly-alpha emitters ($mathrm{<10^{40} erg s^{-1}}$), provided that the faint end of the Ly-alpha luminosity function is steep ($alpha lessapprox -1.8$), it extends down to luminosities lower than $mathrm{10^{38} - 10^{37} erg s^{-1}}$ and the clustering of these Ly-alpha emitters is significant (filling factor $< 1/6$). If these Ly-alpha emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates $mathrm{< 10^{-4} M_odot yr^{-1}}$. These observations provide the first detection of the cosmic web in Ly-alpha emission in typical filamentary environments and the first observational clue for the existence of a large population of ultra low luminosity Ly-alpha emitters at high redshift.
We study the slope, intercept, and scatter of the color-magnitude and color-mass relations for a sample of ten infrared red-sequence-selected clusters at z ~ 1. The quiescent galaxies in these clusters formed the bulk of their stars above z ~ 3 with an age spread {Delta}t ~ 1 Gyr. We compare UVJ color-color and spectroscopic-based galaxy selection techniques, and find a 15% difference in the galaxy populations classified as quiescent by these methods. We compare the color-magnitude relations from our red-sequence selected sample with X-ray- and photometric- redshift-selected cluster samples of similar mass and redshift. Within uncertainties, we are unable to detect any difference in the ages and star formation histories of quiescent cluster members in clusters selected by different methods, suggesting that the dominant quenching mechanism is insensitive to cluster baryon partitioning at z ~ 1.
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