Massive clusters of galaxies have been found that date from as early as 3.9 billion years (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs. Cosmological ...simulations using the current cold dark matter model predict that these systems should descend from 'protoclusters'-early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies that can be observed as luminous quasars and starbursts. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here we report a protocluster region that dates from 1 Gyr (z = 5.3) after the Big Bang. This cluster of massive galaxies extends over more than 13 megaparsecs and contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of more than 4 × 10(11) solar masses of dark and luminous matter in this region, consistent with that expected from cosmological simulations for the earliest galaxy clusters.
We have imaged the dense star-forming regions of Arp 220 and NGC 6240 in the 3 mm band transitions of CO, HCN, HCO+, HNC, and CS at 0 5-0 8 resolution using CARMA. Our data set images all these lines ...at similar resolutions and high sensitivity, and can be used to derive line ratios of faint high excitation lines. In both the nuclei of Arp 220, the HCN/HNC ratios suggest chemistry of X-ray Dominated Regions (XDRs)-a likely signature of an active galactic nucleus. In NGC 6240, there is no evidence of XDR type chemistry, but there the bulk of the molecular gas is concentrated between the nuclei rather than on them. We calculated molecular H2 densities from excitation analysis of each of the molecular species. It appears that the abundances of HNC and HCO+ in Ultra Luminous Infrared Galaxies may be significantly different from those in galactic molecular clouds. The derived H2 volume densities are ∼5 × 104 cm−3 in the Arp 220 nuclei and ∼104 cm−3 in NGC 6240.
We have measured the fraction of bars in nearby spiral galaxies using near-infrared J, H, and K sub(S) images of 151 spiral galaxies from 2MASS. This local sample provides an anchor for the study of ...the evolution of the bar fraction and bar properties with redshift. We identify bars by analyzing the full two-dimensional light distribution and requiring a combined ellipticity and position angle signature. The combined "bar signature" is found in 59% of the galaxies. The bar fraction increases to 67% when we include "candidate" bars, where only the ellipticity signature is present. We also measure the change in the bar fraction as a function of bar size; the bar fraction drops to 31% for bars with a semimajor axis larger than 4 kpc. We find that infrared bars typically extend to one-third of the galactic disk, with a deprojected relative size of (a sub(bar)/R sub(25)) 6 0.3 c 0.2. Early-type spirals host significantly larger bars, consistent with earlier studies. The (a sub(bar)/R sub(25)) is 2 times larger in early types man in late types. The typical bar axial ratio (b/a) is 60.5, with a weak trend of higher axial ratios for larger bars.
We report the serendipitous discovery of a dusty, starbursting galaxy at z = 5.667 (hereafter called CRLE) in close physical association with the "normal" main-sequence galaxy HZ10 at z = 5.654. CRLE ...was identified by detection of C ii, N ii, and CO(2-1) line emission, making it the highest-redshift, most luminous starburst in the COSMOS field. This massive, dusty galaxy appears to be forming stars at a rate of at least 1500 M yr−1 in a compact region only ∼3 kpc in diameter. The dynamical and dust emission properties of CRLE suggest an ongoing merger driving the starburst, which is in a potentially intermediate stage relative to other known dusty galaxies at the same epoch. The ratio of C ii to N ii may suggest that an important (∼15%) contribution to the C ii emission comes from a diffuse ionized gas component, which could be more extended than the dense, starbursting gas. CRLE appears to be located in a significant galaxy overdensity at the same redshift, potentially associated with a large-scale cosmic structure recently identified in a Lyman -emitter survey. This overdensity suggests that CRLE and HZ10 reside in a protocluster environment, offering the tantalizing opportunity to study the effect of a massive starburst on protocluster star formation. Our findings support the interpretation that a significant fraction of the earliest galaxy formation may occur from the inside out, within the central regions of the most massive halos, while rapidly evolving into the massive galaxy clusters observed in the local universe.
ALMA Resolves the Nuclear Disks of Arp 220 Scoville, Nick; Murchikova, Lena; Walter, Fabian ...
The Astrophysical journal,
02/2017, Letnik:
836, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at . The internal gas distribution and kinematics of both galactic nuclei are well resolved for the ...first time. In the west nucleus, the major gas and dust emission extends out to 0 2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor of 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick ( ) at with a dust brightness temperature of ∼147 K. The column of interstellar matter at this nucleus is cm−2, corresponding to ∼900 gr cm−2. The east nucleus is more elongated with radial extent 0 3 or ∼111 pc. The derived kinematics of the nuclear disks provide a good fit to the line profiles, yielding the emissivity distributions, the rotation curves, and velocity dispersions. In the west nucleus, there is evidence of a central Keplerian component requiring a central mass of 8 × 108 . The intrinsic widths of the emission lines are (west) and 120 (east) km s−1. Given the very short dissipation timescales for turbulence ( 105 years), we suggest that the line widths may be due to semicoherent motions within the nuclear disks. The symmetry of the nuclear disk structures is impressive, implying the merger timescale is significantly longer than the rotation period of the disks.
We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ...ionized outflow, has a projected length of ∼300 pc, with a width of ∼50 pc, and a velocity dispersion of ∼40 km s−1, which is consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s−1 pc−1. In this scenario, the gas is approaching an escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO+, CS) are also detected in the molecular outflow: we measure an HCN(1-0)/CO(1-0) line ratio of in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower ( ), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ∼1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.
Abstract
We study the mass–metallicity relation for 19 members of a spectroscopically confirmed protocluster in the COSMOS field at
z
= 2.2 (CC2.2), and compare it with that of 24 similarly selected ...field galaxies at the same redshift. Both samples are H
α
emitting sources, chosen from the HiZELS narrowband survey, with metallicities derived from the
N
2
NII
λ
6584
H
α
line ratio. For the mass-matched samples of protocluster and field galaxies, we find that protocluster galaxies with 10
9.9
M
⊙
≤
M
*
≤ 10
10.9
M
⊙
are metal deficient by 0.10 ± 0.04 dex (2.5
σ
significance) compared to their coeval field galaxies. This metal deficiency is absent for low-mass galaxies,
M
*
< 10
9.9
M
⊙
. Moreover, relying on both spectral energy distribution derived and H
α
(corrected for dust extinction based on M
*
) star formation rates (SFRs), we find no strong environmental dependence of the SFR–
M
*
relation; however, we are not able to rule out the existence of small dependence due to inherent uncertainties in both SFR estimators. The existence of 2.5
σ
significant metal deficiency for massive protocluster galaxies favors a model in which funneling of the primordial cold gas through filaments dilutes the metal content of protoclusters at high redshifts (
z
≳ 2). At these redshifts, gas reservoirs in filaments are dense enough to cool down rapidly and fall into the potential well of the protocluster to lower the gas-phase metallicity of galaxies. Moreover, part of this metal deficiency could be originated from galaxy interactions that are more prevalent in dense environments.
Abstract
The underlying distribution of galaxies’ dust spectral energy distributions (SEDs) (i.e., their spectra reradiated by dust from rest-frame ∼3
μ
m to 3 mm) remains relatively unconstrained ...owing to a dearth of far-IR/(sub)millimeter data for large samples of galaxies. It has been claimed in the literature that a galaxy’s dust temperature—observed as the wavelength where the dust SED peaks (
λ
peak
)—is traced most closely by its specific star formation rate (sSFR) or parameterized “distance” to the SFR–
M
⋆
relation (the galaxy “main sequence”). We present 024 resolved 870
μ
m ALMA dust continuum observations of seven
z
= 1.4–4.6 dusty star-forming galaxies chosen to have a large range of well-constrained luminosity-weighted dust temperatures. We also draw on similar-resolution dust continuum maps from a sample of ALESS submillimeter galaxies from Hodge et al (2016). We constrain the physical scales over which the dust radiates and compare those measurements to characteristics of the integrated SED. We confirm significant correlations of
λ
peak
with both
L
IR
(or SFR) and Σ
IR
(∝SFR surface density). We investigate the correlation between log
10
(
λ
peak
) and log
10
(Σ
IR
) and find the relation to hold as would be expected from the Stefan–Boltzmann law, or the effective size of an equivalent blackbody. The correlations of
λ
peak
with sSFR and distance from the SFR–
M
⋆
relation are less significant than those for Σ
IR
or
L
IR
; therefore, we conclude that the more fundamental tracer of galaxies’ luminosity-weighted integrated dust temperatures are indeed their star formation surface densities in line with local universe results, which relate closely to the underlying geometry of dust in the interstellar medium.
ABSTRACT Our current understanding of galaxy evolution still has many uncertainties associated with the details of the accretion, processing, and removal of gas across cosmic time. The next ...generation of radio telescopes will image the neutral hydrogen (H i) in galaxies over large volumes at high redshifts, which will provide key insights into these processes. We are conducting the COSMOS H i Large Extragalactic Survey (CHILES) with the Karl G. Jansky Very Large Array, which is the first survey to simultaneously observe H i from z = 0 to z ∼ 0.5. Here, we report the highest redshift H i 21 cm detection in emission to date of the luminous infrared galaxy COSMOS J100054.83+023126.2 at z = 0.376 with the first 178 hr of CHILES data. The total H i mass is (2.9 1.0) × 1010M and the spatial distribution is asymmetric and extends beyond the galaxy. While optically the galaxy looks undisturbed, the H i distribution suggests an interaction with a candidate companion. In addition, we present follow-up Large Millimeter Telescope CO observations that show it is rich in molecular hydrogen, with a range of possible masses of (1.8-9.9) × 1010M . This is the first study of the H i and CO in emission for a single galaxy beyond z ∼ 0.2.
We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5 x 10 super(5) M sub(middot in circle) in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC ...4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and super(12)CO (J = 1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H sub(2) mass (or X sub(CO)) for each galaxy is 1-2 x 10 super(20) cm super(-2) (K km s super(-1)) super(-1), all within a factor of two of the Milky Way disk value (~2 x 10 super(20) cm super(-2) (K km s super(-1)) super(-1)). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X sub(CO) trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.
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