38 research outputs found
Effects of Stellar Feedback on Stellar and Gas Kinematics of Star-forming Galaxies at 0.6 < z < 1.0
Recent zoom-in cosmological simulations have shown that stellar feedback can flatten the inner density profile of the dark matter halo in low-mass galaxies. A correlation between the stellar/gas velocity dispersion (Ï star, Ï gas) and the specific star formation rate (sSFR) is predicted as an observational test of the role of stellar feedback in re-shaping the dark matter density profile. In this work we test the validity of this prediction by studying a sample of star-forming galaxies at 0.6 < z < 1.0 from the LEGA-C survey, which provides high signal-to-noise measurements of stellar and gas kinematics. We find that a weak but significant correlation between Ï star (and Ï gas) and sSFR indeed exists for galaxies in the lowest mass bin (M â ⌠1010 M oË). This correlation, albeit with a âŒ35% scatter, holds for different tracers of star formation, and becomes stronger with redshift. This result generally agrees with the picture that at higher redshifts star formation rate was generally higher, and galaxies at M â âČ 1010 M oË have not yet settled into a disk. As a consequence, they have shallower gravitational potentials more easily perturbed by stellar feedback. The observed correlation between Ï star (and Ï gas) and sSFR supports the scenario predicted by cosmological simulations, in which feedback-driven outflows cause fluctuations in the gravitation potential that flatten the density profiles of low-mass galaxies
Recommended from our members
The VIMOS Ultra-Deep Survey: A major merger origin for the high fraction of galaxies at 2 < z < 6 with two bright clumps
(Abridged) The properties of stellar clumps in star forming galaxies and
their evolution over the redshift range are presented
and discussed in the context of the build-up of massive galaxies at early
cosmic times. We use HST/ACS images of galaxies with spectroscopic redshifts
from the VIMOS Ultra Deep Survey (VUDS) to identify clumps within a 20 kpc
radius. We find that the population of galaxies with more than one clump is
dominated by galaxies with two clumps, representing \% of the
population, while the fraction of galaxies with 3, or 4 and more, clumps is
8-11 and 7-9\%, respectively. The fraction of clumpy galaxies is in the range
over , increasing at higher redshifts, indicating that the
fraction of irregular galaxies remains high up to the highest redshifts. The
large and bright clumps (M up to M) are
found to reside predominantly in galaxies with two clumps. Smaller and lower
luminosity clumps () are
found in galaxies with three clumps or more. We interpret these results as
evidence for two different modes of clump formation working in parallel. The
small low luminosity clumps are likely the result of disc fragmentation, with
violent disc instabilities (VDI) forming several long-lived clumps in-situ, as
suggested from simulations. A fraction of these clumps is also likely coming
from minor mergers. The clumps in the dominating population of galaxies with
two clumps are significantly more massive and have properties akin to those in
merging pairs observed at similar redshifts; they appear as more massive than
the most massive clumps observed in VDI numerical simulations
Lyα-Lyman continuum connection in 3:5 †z †4:3 star-forming galaxies from the VUDS survey
© ESO 2018. Context. To identify the galaxies responsible for the reionization of the Universe, we must rely on the investigation of the Lyman continuum (LyC) properties of z . 5 star-forming galaxies, where we can still directly observe their ionizing radiation. Aims. The aim of this work is to explore the correlation between the LyC emission and some of the proposed indirect indicators of LyC radiation at z 4 such as a bright Lyα emission and a compact UV continuum size. Methods. We selected a sample of 201 star-forming galaxies from the Vimos Ultra Deep Survey (VUDS) at 3:5 †z †4:3 in the COSMOS, ECDFS, and VVDS-2h fields, including only those with reliable spectroscopic redshifts, a clean spectrum in the LyC range and clearly not contaminated by bright nearby sources in the same slit. For all galaxies we measured the Lyα EW, the Lyα velocity shift with respect to the systemic redshift, the Lyα spatial extension and the UV continuum effective radius. We then selected different sub-samples according to the properties predicted to be good LyC emission indicators: in particular we created sub-samples of galaxies with EW(Lyα) λ 70, Lyαext †5:7 kpc, rUV †0:30 kpc and jÎvLyαj †200 km s-1. We stacked all the galaxies in each sub-sample and measured the flux density ratio ( fλ(895)= fλ(1470)), that we considered to be a proxy for LyC emission. We then compared these ratios to those obtained for the complementary samples. Finally, to estimate the statistical contamination from lower redshift inter-lopers in our samples, we performed dedicated Monte Carlo simulations using an ultradeep U-band image of the ECDFS field. Results. We find that the stacks of galaxies which are UV compact (rUV †0:30 kpc) and have bright Lyα emission (EW(Lyα) λ 70), have much higher LyC fluxes compared to the rest of the galaxy population. These parameters appear to be good indicators of LyC radiation in agreement with theoretical studies and previous observational works. In addition we find that galaxies with a low Lyα spatial extent (Lyαext †5:7 kpc) have higher LyC flux compared to the rest of the population. Such a correlation had never been analysed before and seems even stronger than the correlation with high EW(Lyα) and small rUV . These results assume that the stacks from all sub-samples present the same statistical contamination from lower redshift interlopers. If we subtract a statistical contamination from low redshift interlopers obtained with the simulations from the flux density ratios ( fλ(895)= fλ(1470)) of the significant sub-samples we find that these samples contain real LyC leaking flux with a very high probability, although the true average escape fractions are very uncertain. Conclusions. Our work indicates that galaxies with very high EW(Lyα), small Lyαext and small rUV are very likely the best candidates to show Lyman continuum radiation at z 4 and could therefore be the galaxies that have contributed most to reionisation
RELICS: spectroscopy of gravitationally lensed z â 2 reionization-era analogues and implications for CâIII] detections at z > 6
Recent observations have revealed the presence of strong CâIII] emission (EWCIII]>20 Ă
) in z > 6 galaxies, the origin of which remains unclear. In an effort to understand the nature of these line emitters, we have initiated a survey targeting CâIII] emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2â8 Ă 107 Mâ) and J125-band flux excesses indicative of intense [OâIII] + HâÎČ emission (EW[OIII]+HÎČ = 500â2000 Ă
), similar to what has been observed at z > 6. We detect CâIII] emission in three of the four sources, with the CâIII] EW reaching values seen in the reionization era (EWCIII]â17â22 Ă
) in the two sources with the strongest optical line emission (EW[OIII]+HÎČâ2000 Ă
). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest CâIII] emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense CâIII] and optical line emission for extremely young (2â3 Myr) and metal-poor (0.06â0.08 Zâ) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which CâIII] has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using CâIII] to measure redshifts of objects with IRAC excesses indicating EW[OIII]+HÎČâ2000 Ă
, providing a method of spectroscopic confirmation independent of Lyâα
Characterization of star-forming dwarf galaxies at 0.1 âČ z âČ 0.9 in VUDS: Probing the low-mass end of the mass-metallicity relation
We present the discovery and spectrophotometric characterization of a large
sample of 164 faint ( - mag) star-forming dwarf galaxies
(SFDGs) at redshift selected by the presence of
bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). We
investigate their integrated physical properties and ionization conditions,
which are used to discuss the low-mass end of the mass-metallicity relation
(MZR) and other key scaling relations. We use optical VUDS spectra in the
COSMOS, VVDS-02h, and ECDF-S fields, as well as deep multiwavelength
photometry, to derive stellar masses, star formation rates (SFR) and gas-phase
metallicities. The VUDS SFDGs are compact (median kpc),
low-mass ( ) galaxies with a wide range of
star formation rates (SFR() ) and
morphologies. Overall, they show a broad range of subsolar metallicities
(12+log(O/H)=-; ). The MZR
of SFDGs shows a flatter slope compared to previous studies of galaxies in the
same mass range and redshift. We find the scatter of the MZR partly explained
in the low mass range by varying specific SFRs and gas fractions amongst the
galaxies in our sample. Compared with simple chemical evolution models we find
that most SFDGs do not follow the predictions of a "closed-box" model, but
those from a gas regulating model in which gas flows are considered. While
strong stellar feedback may produce large-scale outflows favoring the cessation
of vigorous star formation and promoting the removal of metals, younger and
more metal-poor dwarfs may have recently accreted large amounts of fresh, very
metal-poor gas, that is used to fuel current star formation
Recommended from our members
The VIMOS Ultra Deep Survey: The role of HI kinematics and HI column density on the escape of Lyα photons in star-forming galaxies at 2 < z < 4
© 2017 ESO. Aims. We wish to assess the role of kinematics and neutral hydrogen column density in the escape and distribution of Lya photons. Methods. We selected a sample of 76 Lya emitting galaxies from the VIMOS Ultra Deep Survey (VUDS) at 2 = z = 4. We estimated the velocity of the neutral gas flowing out of the interstellar medium as the velocity offset, ÎŽv, between the systemic redshift (zsys) and the center of low-ionization absorption line systems (LIS). To increase the S/N of VUDS spectra, we stacked subsamples defined based on median values of their photometric and spectroscopic properties. We measured the systemic redshift from the rest-frame UV spectroscopic data using the CIII]1908 nebular emission line, and we considered SiII1526 as the highest signal-to-noise LIS line. We calculated the Lya peak shift with respect to the zsys, the EW(Lya), and the Lya spatial extension, Ext(Lya-C), from the in the 2D stacked spectra. Results. The galaxies that are faint in the rest-frame UV continuum, strong in Lya and CIII] , with compact UV morphology, and localized in an underdense environment are characterized by outflow velocities of the order of a few hundreds of km s -1 . The subsamples with smaller ÎŽv are characterized by larger Lya peak shifts, larger Ext(Lya-C), and smaller EW(Lya). In general we find that EW(Lya) anti-correlates with Ext(Lya-C) and Lya peak shift. Conclusions. We interpret these trends using a radiative-transfer shell model. The model predicts that an HI gas with a column density larger than 1020 cm -2 is able to produce Lya peak shifts larger than > 300 km s -1 . An ISM with this value of NHI would favour a large amount of scattering events, especially when the medium is static, so it can explain large values of Ext(Lya-C) and small EW(Lya). On the contrary, an ISM with a lower NHI, but large velocity outflows would lead to a Lya spatial profile peaked at the galaxy center (i.e. low values of Ext(Lya-C)) and to a large EW(Lya), as we see in our data. Our results and their interpretation via radiative-transfer models tell us that it is possible to use Lya to study the properties of the HI gas. Also, the fact that Lya emitters are characterized by large ÎŽv could give hints about their stage of evolution in the sense that they could be experiencing short bursts of star formation that push strong outflows.This work is supported by funding from the European Research Council Advanced Grant ERCâ2010âAdGâ268107âEARLY and by INAF Grants PRIN 2010, PRIN 2012, and PICS 2013. This work is based on data products made available at the CESAM data center, Laboratoire dâAstrophysique de Marseille, France. R.A. acknowledges support from the ERC Advanced Grant 695671 âQUENCHâ and I.O. from the Czech Science Foundation grant 17-06217Y
The ALPINE-ALMA [C ii] Survey: Size of Individual Star-forming Galaxies at z = 4-6 and Their Extended Halo Structure
We present the physical extent of [CII] 158um line-emitting gas from 46
star-forming galaxies at z=4-6 from the ALMA Large Program to INvestigate CII
at Early Times (ALPINE). Using exponential profile fits, we measure the
effective radius of the [CII] line (r_e,[CII]) for individual galaxies and
compare them with the rest-frame ultra-violet (UV) continuum (r_e,UV) from
Hubble Space Telescope images. The effective radius r_e,[CII] exceeds r_e,UV by
factors of ~2-3 and the ratio of r_e,[CII]/r_e,UV increases as a function of
M_star. We do not find strong evidence that [CII] line, the rest-frame UV, and
FIR continuum are always displaced over ~ 1-kpc scale from each other. We
identify 30% of isolated ALPINE sources as having an extended [CII] component
over 10-kpc scales detected at 4.1-10.9 beyond the size of
rest-frame UV and far-infrared (FIR) continuum. One object has tentative
rotating features up to ~10-kpc, where the 3D model fit shows the rotating
[CII]-gas disk spread over 4 times larger than the rest-frame UV-emitting
region. Galaxies with the extended [CII] line structure have high
star-formation rate (SFR), stellar mass (M_star), low Lya equivalent-width, and
more blue-shifted (red-shifted) rest-frame UV metal absorption (Lya line), as
compared to galaxies without such extended [CII] structures. Although we cannot
rule out the possibility that a selection bias towards luminous objects may be
responsible for such trends, the star-formation driven outflow also explains
all these trends. Deeper observations are essential to test whether the
extended [CII] line structures are ubiquitous to high-z star-forming galaxies.ERC
STF
The ALPINE-ALMA [CII] survey. Little to no evolution in the [CII]-SFR relation over the last 13 Gyr
The [CII] 158 micron line is one of the strongest IR emission lines, which
has been shown to trace the star-formation rate (SFR) of galaxies in the nearby
Universe and up to . Whether this is also the case at higher redshift
and in the early Universe remains debated. The ALPINE survey, which targeted
118 star-forming galaxies at , provides a new opportunity to
examine this question with the first statistical dataset. Using the ALPINE data
and earlier measurements from the literature we examine the relation between
the [CII] luminosity and the SFR over the entire redshift range from . ALPINE galaxies, which are both detected in [CII] and dust continuum,
show a good agreement with the local L([CII])-SFR relation. Galaxies undetected
in the continuum with ALMA are found to be over-luminous in [CII], when the UV
SFR is used. After accounting for dust-obscured star formation, by an amount
SFR(IR)SFR(UV) on average, which results from two different stacking
methods and SED fitting, the ALPINE galaxies show an L([CII])-SFR relation
comparable to the local one. When [CII] non-detections are taken into account,
the slope may be marginally steeper at high-z, although this is still somewhat
uncertain. When compared in a homogeneous manner, the [CII] measurements
(detections and upper limits) do not behave very differently from the data. We find a weak dependence of L([CII])/SFR on the Lyman-alpha
equivalent width. Finally, we find that the ratio L([CII])/LIR for the ALPINE sources, comparable to that of "normal" galaxies
at lower redshift. Our analysis, which includes the largest sample (
galaxies) of [CII] measurements at available so far, suggests no or
little evolution of the L([CII])-SFR relation over the last 13 Gyr of cosmic
time.STFC
ER
The ALPINE-ALMA [CII] survey: Dust attenuation properties and obscured star formation at z âŒ4.4-5.8
We present dust attenuation properties of spectroscopically confirmed star
forming galaxies on the main sequence at redshift ~4.4-5.8. Our analyses are
based on the far infrared continuum observations of 118 galaxies at rest-frame
obtained with the ALMA large program ALPINE. We study the
connection between the UV spectral slope (), stellar mass (),
and infrared excess (IRX). Twenty-three galaxies are
individually detected in the continuum at significance. We
perform a stacking analysis using both detections and non-detections to study
the average dust attenuation properties at z~4.4-5.8. The individual detections
and stacks show that the IRX- relation at z~5 is consistent with a
steeper dust attenuation curve than typically found at lower redshifts (z<4).
The attenuation curve is similar to or even steeper than that of the extinction
curve of the Small Magellanic Cloud (SMC). This systematic change of the
IRX- relation as a function of redshift suggests an evolution of dust
attenuation properties at . Similarly, we find that our galaxies have
lower IRX values up to 1 dex on average at fixed mass compared to previously
studied IRX- relations at , albeit with significant
scatter. This implies a lower obscured fraction of star-formation than at lower
redshifts. Our results suggest that dust properties of UV-selected star forming
galaxies at are characterised by (i) a steeper attenuation curve
than at , and (ii) a rapidly decreasing dust obscured fraction of
star formation as a function of redshift. Nevertheless, even among this
UV-selected sample, massive galaxies () at z~5-6
already exhibit an obscured fraction of star formation of ,
indicating a rapid build-up of dust during the epoch of reionization.STFC
ER
AGN-enhanced outflows of low-ionization gas in star-forming galaxies at 1.7 < z < 4.6
Fast and energetic winds are invoked by galaxy formation models as essential processes in the evolution of galaxies. These outflows can be powered either by star formation (SF) and/or active galactic nucleus (AGN) activity, but the relative dominance of the two mechanisms is still under debate. We use spectroscopic stacking analysis to study the properties of the low-ionization phase of the outflow in a sample of 1330 star-forming galaxies (SFGs) and 79 X-ray-detected (1042 < LX < 1045âerg sâ1) Type 2 AGN at 1.7 < z < 4.6 selected from a compilation of deep optical spectroscopic surveys, mostly zCOSMOS-Deep and VIMOS Ultra Deep Survey (VUDS). We measure mean velocity offsets of âŒâ 150âkmâsâ1 in the SFGs, while in the AGN sample the velocity is much higher (âŒâ 950âkmâsâ1), suggesting that the AGN is boosting the outflow up to velocities that could not be reached only with the SF contribution. The sample of X-ray AGN has on average a lower SF rate than non-AGN SFGs of similar mass: this, combined with the enhanced outflow velocity in AGN hosts, is consistent with AGN feedback in action. We further divide our sample of AGN into two X-ray luminosity bins: we measure the same velocity offsets in both stacked spectra, at odds with results reported for the highly ionized phase in local AGN, suggesting that the two phases of the outflow may be mixed only up to relatively low velocities, while the highest velocities can be reached only by the highly ionized phase.This work is supported by funding from the European Research Council Advanced Grant ERCâ2010âAdGâ268107âEARLY and by INAF Grants PRIN 2010, PRIN 2012 and PICS 2013. AC, OC, and MT acknowledge the grant MIUR PRIN 2010â2011. MB acknowledges support from the FP7 grant âeEASyâ: (CIG 321913). RA acknowledges support from the ERC Advanced Grant 695671 âQUENCHâ. We acknowledge the grants ASI n.I/023/12/0 âAttivitĂ relative alla fase B2/C per la missione Euclidâ and MIUR PRIN 2010-2011 âThe dark Universe and the cosmic evolution of baryons: from current surveys to Euclidâ and PRIN MIUR 2015 âCosmology and Fundamental Physics: illuminating the Dark Universe with Euclidâ