73 research outputs found
The properties of the star-forming interstellar medium at z=0.84-2.23 from HiZELS: mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies
We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine Hïżœ-selected galaxies at z =0.84â2.23 drawn from the HiZELS narrow-band survey.
These galaxies have star-formation rates of 1â27Mâ yrâ1 and are therefore representative of the typical high-redshift star-forming population. Our ïżœkpc-scale resolution
observations show that approximately half of the sample have dynamics suggesting that the ionised gas is in large, rotating disks. We model their velocity fields to infer
the inclination-corrected, asymptotic rotational velocities.We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor 2.5 between z =2 and z =0, whilst the rest-frame B-band luminosity has decreased by a factor ïżœ6 over the same
period. Together, these demonstrate a change in mass-to-light ratio in the B-band of ïżœ(M/ LB) / (M/ LB)z=0 ïżœ3.5 between z =1.5 and z =0, with most of the evolution occuring below z =1. We also use the spatial variation of [Nii] /Hïżœ to show that the metallicity of the ionised gas in these galaxies declines monotonically with galactocentric radius, with an average ïżœlog(O/H) /ïżœR=â0.027±0.005 dex kpcâ1. This gradient is consistent with predictions for high-redshift disk galaxies from cosmologically based hydrodynamic simulations.
Key words: galaxies: evolution â galaxies: formation â galaxies: high-redshif
An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: halo masses for submillimetre galaxies
We present an analysis of the spatial clustering of a large sample of high-resolution, interferometically identified, submillimetre galaxies (SMGs). We measure the projected cross-correlation function of âŒ350 SMGs in the UKIDSS Ultra Deep-Survey Field across a redshift range of z = 1.5â3 utilizing a method that incorporates the uncertainties in the redshift measurements for both the SMGs and cross-correlated galaxies through sampling their full probability distribution functions. By measuring the absolute linear bias of the SMGs, we derive halo masses of log10(Mhalo[hâ1Mâ]) ⌠12.8 with no evidence of evolution in the halo masses with redshift, contrary to some previous work. From considering models of halo mass growth rates, we predict that the SMGs will reside in haloes of mass log10(Mhalo[hâ1Mâ]) ⌠13.2 at z = 0, consistent with the expectation that the majority of z = 1.5â3 SMGs will evolve into present-day spheroidal galaxies. Finally, comparing to models of stellar-to-halo mass ratios, we show that SMGs may correspond to systems that are maximally efficient at converting their gas reservoirs into stars. We compare them to a simple model for gas cooling in haloes that suggests that the unique properties of the SMG population, including their high levels of star formation and their redshift distribution, are a result of the SMGs being the most massive galaxies that are still able to accrete cool gas from their surrounding intragalactic medium
Tracing the evolution of dust-obscured activity using sub-millimetre galaxy populations from STUDIES and AS2UDS
We analyse the physical properties of 121 SNRââ„â5 sub-millimetre galaxies (SMGs) from the STUDIES 450âÎŒm survey. We model their UV-to-radio spectral energy distributions using MAGPHYS+photo-z and compare the results to similar modelling of 850âÎŒm-selected SMG sample from AS2UDS, to understand the fundamental physical differences between the two populations at the observed depths. The redshift distribution of the 450-ÎŒm sample has a median of z = 1.85â±â0.12 and can be described by strong evolution of the far-infrared luminosity function. The fainter 450-ÎŒm sample has âŒ14 times higher space density than the brighter 850-ÎŒm sample at zââČâ2, and a comparable space density at z = 2â3, before rapidly declining, suggesting LIRGs are the main obscured population at z ⌠1â2, while ULIRGs dominate at higher redshifts. We construct rest-frame âŒ180-ÎŒm-selected and dust-mass-matched samples at z = 1â2 and z = 3â4 from the 450 and 850-ÎŒm samples, respectively, to probe the evolution of a uniform sample of galaxies spanning the cosmic noon era. Using far-infrared luminosity, dust masses, and an optically thick dust model, we suggest that higher redshift sources have higher dust densities due to inferred dust continuum sizes which are roughly half of those for the lower redshift population at a given dust mass, leading to higher dust attenuation. We track the evolution in the cosmic dust mass density and suggest that the dust content of galaxies is governed by a combination of both the variation of gas content and dust destruction time-scale
Stellar feedback in a clumpy galaxy at z ⌠3.4
Giant star-forming regions (clumps) are widespread features of galaxies at z â 1â4. Theory predicts that they can play a crucial role in galaxy evolution, if they survive to stellar feedback for >50 Myr. Numerical simulations show that clumpsâ survival depends on the stellar feedback recipes that are adopted. Up to date, observational constraints on both clumpsâ outflows strength and gas removal time-scale are still uncertain. In this context, we study a line-emitting galaxy at redshift z â 3.4 lensed by the foreground galaxy cluster Abell 2895. Four compact clumps with sizes âČ280 pc and representative of the low-mass end of clumpsâ mass distribution (stellar masses âČ2 Ă 108âMâ) dominate the galaxy morphology. The clumps are likely forming stars in a starbursting mode and have a young stellar population (âŒ10 Myr). The properties of the Lyman-α (Lyα) emission and nebular far-ultraviolet absorption lines indicate the presence of ejected material with global outflowing velocities of âŒ200â300 kmâsâ1. Assuming that the detected outflows are the consequence of star formation feedback, we infer an average mass loading factor (η) for the clumps of âŒ1.8â2.4 consistent with results obtained from hydrodynamical simulations of clumpy galaxies that assume relatively strong stellar feedback. Assuming no gas inflows (semiclosed box model), the estimates of η suggest that the time-scale over which the outflows expel the molecular gas reservoir (â7 Ă 108âMâ) of the four detected low-mass clumps is âČ50 Myr
An ALMA/NOEMA survey of the molecular gas properties of high-redshift star-forming galaxies
We have used ALMA and NOEMA to study the molecular gas reservoirs in 61 ALMA-identified submillimetre galaxies (SMGs) in the COSMOS, UDS, and ECDFS fields. We detect 12CO (â Jup= 2â5) emission lines in 50 sources, and [CâI](3P1âââ3P0) emission in eight, at z= 1.2â4.8 and with a median redshift of 2.9â±â0.2. By supplementing our data with literature sources, we construct a statistical CO spectral line energy distribution and find that the 12CO line luminosities in SMGs peak at Jup ⌠6, consistent with similar studies. We also test the correlations of the CO, [CâI], and dust as tracers of the gas mass, finding the three to correlate well, although the CO and dust mass as estimated from the 3-mm continuum are preferable. We estimate that SMGs lie mostly on or just above the star-forming main sequence, with a median gas depletion timescale, tdep = Mgas/SFR, of 210â±â40âMyr for our sample. Additionally, tdep declines with redshift across z ⌠1â5, while the molecular gas fraction, ÎŒgas = Mgas/M*, increases across the same redshift range. Finally, we demonstrate that the distribution of total baryonic mass and dynamical line width, MbaryonâÏ, for our SMGs is consistent with that followed by early-type galaxies in the Coma cluster, providing strong support to the suggestion that SMGs are progenitors of massive local spheroidal galaxies. On the basis of this, we suggest that the SMG populations above and below an 870-ÎŒm flux limit of S870 ⌠5âmJy may correspond to the division between slow and fast rotators seen in local early-type galaxies
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
Resolving the ISM at the Peak of Cosmic Star Formation with ALMA: The Distribution of CO and Dust Continuum in z similar to 2.5 Submillimeter Galaxies
We use Atacama Large Millimeter Array (ALMA) observations of four submillimeter galaxies (SMGs) at z ~ 2â3 to investigate the spatially resolved properties of the interstellar medium (ISM) at scales of 1â5 kpc (0farcs1â0farcs6). The velocity fields of our sources, traced by the 12CO(J = 3â2) emission, are consistent with disk rotation to the first order, implying average dynamical masses of ~3 Ă 1011 within two half-light radii. Through a Bayesian approach we investigate the uncertainties inherent to dynamically constraining total gas masses. We explore the covariance between the stellar mass-to-light ratio and CO-to-H2 conversion factor, α CO, finding values of for dark matter fractions of 15%. We show that the resolved spatial distribution of the gas and dust continuum can be uncorrelated to the stellar emission, challenging energy balance assumptions in global SED fitting. Through a stacking analysis of the resolved radial profiles of the CO(3â2), stellar, and dust continuum emission in SMG samples, we find that the cool molecular gas emission in these sources (radii ~5â14 kpc) is clearly more extended than the rest-frame ~250 ÎŒm dust continuum by a factor >2. We propose that assuming a constant dust-to-gas ratio, this apparent difference in sizes can be explained by temperature and optical depth gradients alone. Our results suggest that caution must be exercised when extrapolating morphological properties of dust continuum observations to conclusions about the molecular gas phase of the interstellar medium (ISM)
Integral field spectroscopy of H alpha emission in cooling flow cluster cores: disturbing the molecular gas reservoir
We present optical integral field spectroscopy of the H-alpha-luminous (>1E42
erg/s) central cluster galaxies in the cores of the cooling flows A1664, A1835,
A2204 and Zw8193. From the [NII]+H-alpha complex we derive 2-D views of the
distribution and kinematics of the emission line gas, and further diagnostics
from the [SII] and [OI] lines. The H-alpha emission shows a variety of
disturbed morphologies with velocity gradients and splittings of several
hundred km/s on scales of 20 kpc or more. Despite the small sample size, there
are some generic features. The most disturbed H-alpha emission appears to be
associated with secondary galaxies within 10-20 kpc (projected) of the central
galaxy and close in velocity to the H-alpha. The global H-alpha kinematics
match those of CO(1-0) emission in single-dish data. The [NII]/H-alpha,
[SII]/H-alpha and [OI]/H-alpha ratios vary little with position, local H-alpha
surface brightness or between clusters. We propose that the H-alpha and CO
emission arise in molecular clouds heated by a starburst which has been
triggered by interaction with a secondary galaxy. Such CO emission is known to
trace massive (>1E10 M_sun) compact (<20 kpc) reservoirs of cool molecular gas,
which an infalling galaxy may disturb, distorting the H-alpha morphology and
initiating widespread star formation. We suggest that cloud-cloud collisions in
the undisturbed molecular gas reservoir might be an important excitation source
for the emission line gas in the cores of lower H-alpha luminosity cluster
cores with less intense star formation (abridged).Comment: 15 pages, 16 figures (7 with essential colour), accepted by MNRA
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A gravitationally boosted MUSE survey for emission-line galaxies at z greater than or similar to 5 behind the massive cluster RCS 0224
We present a Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) survey of lensed high-redshift galaxies behind the z = 0.77 cluster RCS 0224â0002. We study the detailed internal properties of a highly magnified (ÎŒ ⌠29) z = 4.88 galaxy seen through the cluster. We detect widespread nebular C IV λλ1548,1551 Ă
emission from this galaxy as well as a bright Lyα halo with a spatially uniform wind and absorption profile across 12 kpc in the image plane. Blueshifted high- and low-ionization interstellar absorption indicate the presence of a high-velocity outflow (Îv ⌠300âkmâsâ 1) from the galaxy. Unlike similar observations of galaxies at z ⌠2 â 3, the Lyα emission from the halo emerges close to the systemic velocity â an order of magnitude lower in velocity offset than predicted in âshellâ-like outflow models. To explain these observations, we favour a model of an outflow with a strong velocity gradient, which changes the effective column density seen by the Lyα photons. We also search for high-redshift Lyα emitters and identify 14 candidates between z = 4.8 â 6.6, including an overdensity at z = 4.88, of which only one has a detected counterpart in Hubble Space Telescope/Advanced Camera for Surveys+Wide Field Camera 3 imaging
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