36 research outputs found
ALMACAL VI: Molecular gas mass density across cosmic time via a blind search for intervening molecular absorbers
We are just starting to understand the physical processes driving the dramatic change in cosmic star-formation rate between z ⌠2 and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, thanks to the large redshift path surveyed (Îz = 182), we provide constraints on the molecular column density distribution function beyond z ⌠0. In addition, we probe column densities of N(H2) > 1016 atoms cmâ2, five orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of Ï(H2) âČ 108.3MâMpcâ3 at 0 < z †1.7 already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star-formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to z ⌠2
The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE
We present a multiwavelength analysis of the core of the massive galaxy cluster MACS J0417.5.1154 (z = 0.441). Our analysis takes advantage of Very Large Telescope/Multi-Unit Spectroscopic Explorer observations which allowthe spectroscopic confirmation of three strongly lensed systems. System #1, nicknamed The Doughnut, consists of three images of a complex ring galaxy at z = 0.8718 and a fourth, partial and radial image close to the brightest cluster galaxy (BCG) only discernible thanks to its strong [O II] line emission. The best-fitting mass model (rms of 0.38 arcsec) yields a two-dimensional enclosed mass of M(R < 200 kpc) = (1.77 ± 0.03) Ă 10 14M â and almost perfect alignment between the peaks of the BCG light and the dark matter of (0.5 ± 0.5) arcsec. We observe a significant misalignment when system #1 radial image is omitted. The result serves as an important caveat for studies of BCG-dark-matter offsets in galaxy clusters. Using Chandra to map the intracluster gas, we observe an offset between gas and dark matter of (1.7 ± 0.5) arcsec, and excellent alignment of the X-ray peak with the location of optical emission line associated with the BCG. We interpret all observational evidences in the framework of ongoing cluster merger activity, noting specifically that the coincidence between the gas and optical line peaks may be evidence of dense, cold gas cooled directly from the intracluster gas. Finally, we measure the surface area, Ï ÎŒ, above a given magnification factor ÎŒ, a metric to estimate the lensing power of a lens, Ï(ÎŒ > 3) = 0.22 arcmin 2, which confirms MACS J0417 as an efficient gravitational lens. </p
KURVS: The outer rotation curve shapes and dark matter fractions of star-forming galaxies
We present first results from the KMOS Ultra-deep Rotation Velocity Survey
(KURVS), aimed at studying the outer rotation curves shape and dark matter
content of 22 star-forming galaxies at . These galaxies represent
`typical' star-forming discs at , being located within the
star-forming main sequence and stellar mass-size relation with stellar masses
log. We extract
individual rotation curves out to 4 times the effective radius, on average, or
kpc. Most rotation curves are flat or rising between three- and
six-disc scale radii. Only three objects with dispersion-dominated dynamics
() have declining outer rotation curves at more
than 5 significance. After accounting for seeing and pressure support,
the nine rotation-dominated discs with have
average dark matter fractions of at the effective radius, similar
to local discs. Together with previous observations of star-forming galaxies at
cosmic noon, our measurements suggest a trend of declining dark matter fraction
with increasing stellar mass and stellar mass surface density at the effective
radius. Simulated EAGLE galaxies are in quantitative agreement with
observations up to log, and over-predict the dark matter fraction of galaxies with higher
mass surface densities by a factor of . We conclude that the dynamics
of typical rotationally-supported discs at is dominated by dark
matter from effective radius scales, in broad agreement with cosmological
models. The tension with observations at high stellar mass surface density
suggests that the prescriptions for baryonic processes occurring in the most
massive galaxies (such as bulge growth and quenching) need to be reassessed.Comment: 23 pages, 9 figures. Resubmitted to MNRAS after addressing the
referee's comments. Abstract slightly modified to compile with the arXiv
formattin
The physical scale of the far-infrared emission in the most luminous submillimetre galaxies II: evidence for merger-driven star formation
We present high-resolution 345 GHz interferometric observations of two
extreme luminous (L_{IR}>10^{13} L_sun), submillimetre-selected galaxies (SMGs)
in the COSMOS field with the Submillimeter Array (SMA). Both targets were
previously detected as unresolved point-sources by the SMA in its compact
configuration, also at 345 GHz. These new data, which provide a factor of ~3
improvement in resolution, allow us to measure the physical scale of the
far-infrared in the submillimetre directly. The visibility functions of both
targets show significant evidence for structure on 0.5-1 arcsec scales, which
at z=1.5 translates into a physical scale of 5-8 kpc. Our results are
consistent with the angular and physical scales of two comparably luminous
objects with high-resolution SMA followup, as well as radio continuum and CO
sizes. These relatively compact sizes (<5-10 kpc) argue strongly for
merger-driven starbursts, rather than extended gas-rich disks, as the preferred
channel for forming SMGs. For the most luminous objects, the derived sizes may
also have important physical consequences; under a series of simplifying
assumptions, we find that these two objects in particular are forming stars
close to or at the Eddington limit for a starburst.Comment: 9 pages, 3 Figures, submitted to MNRA
Molecular gas content in typical L* galaxies at z ⌠1.5 â 3
To extend the molecular gas measurements to typical L* star-forming galaxies (SFGs) at z ⌠1.5 â 3, we have observed CO emission for five strongly-lensed galaxies selected from the Herschel Lensing Survey. The combined sample of our L* SFGs with CO-detected SFGs at z >1 from the literature shows a large spread in star formation efficiency (SFE). We find that this spread in SFE is due to variations of several physical parameters, primarily the specific star formation rate, but also stellar mass and redshift. An increase of the molecular gas fraction (f gas) is observed from z ⌠0.2 to z ⌠1.2, followed by a quasi non-evolution toward higher redshifts, as found in earlier studies. We provide the first measure of f gas of z >1 SFGs at the low-stellar mass end between 109.4 < Mâ/Mâ < 109.9, which shows a clear f gas uptur
Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter galaxy that is invisible to HST
We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and
SST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through
the massive cluster lens A1489. These SMA-located sources both lie at z=4.26
and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break
galaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam
observations. We investigate their stellar, ISM, and dynamical properties,
including a pixel-level SED analysis to derive sub-kpc-resolution stellar-mass
and Av maps. We find that 850.1 is one of the most massive and highly obscured,
Av~5, galaxies known at z>4 with M*~10^11.8 Mo (likely forming at z>6), and
850.2 is one of the least massive and least obscured, Av~1, members of the z>4
dusty star-forming population. The diversity of these two dust-mass-selected
galaxies illustrates the incompleteness of galaxy surveys at z>3-4 based on
imaging at <2um, the longest wavelengths feasible from HST or the ground. The
resolved mass map of 850.1 shows a compact stellar mass distribution,
Re(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches both
the properties of massive, quiescent galaxies at z~1.5 and ultra-massive
early-type galaxies at z~0. We suggest that 850.1 is the central galaxy of a
group in which 850.2 is a satellite that will likely merge in the near future.
The stellar morphology of 850.1 shows arms and a linear bar feature which we
link to the active dynamical environment it resides within.Comment: Submitted to ApJ, comments welcome
Hidden Giants in JWST's PEARLS: An Ultramassive z = 4.26 Submillimeter Galaxy that Is Invisible to HST
We present a multiwavelength analysis using the Submillimeter Array (SMA), James Clerk Maxwell Telescope, NOEMA, JWST, the Hubble Space Telescope (HST), and the Spitzer Space Telescope of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A 1489. These SMA-located sources both lie at z = 4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at âČ 2 ÎŒm, even with deep JWST/NIRCam observations. We investigate their stellar, interstellar medium, and dynamical properties, including a pixel-level spectral energy distribution analysis to derive subkiloparsec-resolution stellar-mass and A V maps. We find that 850.1 is one of the most massive and highly obscured, A V ⌠5, galaxies known at z > 4 with M * âŒ1011.8 M â (likely forming at z > 6), and 850.2 is one of the least massive and least obscured, A V ⌠1, members of the z > 4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z âł 3â4 based on imaging at âČ 2 ÎŒm, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar-mass distribution, Remass âŒ1 kpc, but its expected evolution means that it matches both the properties of massive, quiescent galaxies at z ⌠1.5 and ultramassive early-type galaxies at z ⌠0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature that we link to the active dynamical environment it resides within
Prime Focus Spectrograph (PFS) for the Subaru Telescope: Overview, recent progress, and future perspectives
PFS (Prime Focus Spectrograph), a next generation facility instrument on the
8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed,
optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394
reconfigurable fibers will be distributed over the 1.3 deg field of view. The
spectrograph has been designed with 3 arms of blue, red, and near-infrared
cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure
at a resolution of ~1.6-2.7A. An international collaboration is developing this
instrument under the initiative of Kavli IPMU. The project is now going into
the construction phase aiming at undertaking system integration in 2017-2018
and subsequently carrying out engineering operations in 2018-2019. This article
gives an overview of the instrument, current project status and future paths
forward.Comment: 17 pages, 10 figures. Proceeding of SPIE Astronomical Telescopes and
Instrumentation 201
The ALMA Spectroscopic Survey in the HUDF: CO Luminosity Functions and the Molecular Gas Content of Galaxies through Cosmic History
We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of Ï(H2). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ~2 to the local universe. Based on Schechter fits, we estimate that our observations recover the majority (up to ~90%, depending on the assumptions on the faint end) of the total cosmic CO luminosity at z = 1.0â3.1. After correcting for CO excitation, and adopting a Galactic CO-to-H2 conversion factor, we constrain the evolution of the cosmic molecular gas density Ï(H2): this cosmic gas density peaks at z ~ 1.5 and drops by a factor of to the value measured locally. The observed evolution in Ï(H2), therefore, closely matches the evolution of the cosmic star formation rate density Ï SFR. We verify the robustness of our result with respect to assumptions on source inclusion and/or CO excitation. As the cosmic star formation history can be expressed as the product of the star formation efficiency and the cosmic density of molecular gas, the similar evolution of Ï(H2) and Ï SFR leaves only little room for a significant evolution of the average star formation efficiency in galaxies since z ~ 3 (85% of cosmic history)