Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSEEDisCS II. Molecular gas in galaxy clusters and their large scale structure: low gas fraction galaxies, the case of CL1301.7$-$1139
63
0
0.0
(
0
)
Added by
Damien Sp\\'erone-Longin
Publication date
2021
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
This paper is the second of a series that tackles the properties of molecular gas in galaxies residing in clusters and their related large-scale structures. Out of 21 targeted fields, 19 galaxies were detected in CO(3-2) with the Atacama Large Millimeter Array (ALMA), including two detections within a single field. These galaxies are either bona fide members of the CL1301.7$-$1139 cluster ($z=0.4828$, $sigma_{cl}=681$ km s$^{-1}$), or located within $sim 7 times R_{200}$, its virial radius. They have been selected to sample the range of photometric local densities around CL1301.7$-$1139, with stellar masses above log($M_{rm star}$) = 10, and to be located in the blue clump of star-forming galaxies derived from the $u$, $g$, and $i$ photometric bands. Unlike previous works, our sample selection does not impose a minimum star formation rate or detection in the far-infrared. As such and as much as possible, it delivers an unbiased view of the gas content of normal star-forming galaxies at $z sim 0.5$. Our study highlights the variety of paths to star formation quenching, and most likely the variety of physical properties (i.e. temperature, density) of the corresponding galaxys cold molecular gas. Just as in the case of CL1411.1$-$1148, although to a smaller extent, we identify a number of galaxies with lower gas fraction than classically found in other surveys. These galaxies can still be on the star-forming main sequence. When these galaxies are not inside the cluster virialised region, we provide hints that they are linked to their infall regions within $sim 4 times R_{200}$.
rate research
Read More
We investigate how the galaxy reservoirs of molecular gas fuelling star formation are transformed while the host galaxies infall onto galaxy cluster cores. As part of the Spatially Extended ESO Distant Cluster Survey (SEEDisCS), we present CO(3-2) observations of 27 star-forming galaxies obtained with the Atacama Large Millimeter Array (ALMA). These sources are located inside and around CL1411.1$-$1148 at $z=0.5195$, within five times the cluster virial radius. These targets were selected to have stellar masses M$_{rm star}$), colours, and magnitudes similar to those of a field comparison sample at similar redshift drawn from the Plateau de Bure high-$z$ Blue Sequence Survey (PHIBSS2). We compare the cold gas fraction ($mu_{rm H_2}=$ M$_{rm H_2}$/M$_{rm star}$), specific star formation rates (SFR/M$_{rm star}$) and depletion timescales ($t_{rm depl}=$ M$_{rm H_2}$/SFR) of our main-sequence galaxies to the PHIBSS2 subsample. While the most of our galaxies (63%) are consistent with PHIBSS2, the remainder fall below the relation between $mu_mathrm{H_2}$ and M$_{rm star}$ of the PHIBSS2 galaxies at $zsim0.5$. These low-$mu_mathrm{H_2}$ galaxies are not compatible with the tail of a Gaussian distribution, hence they correspond to a new population of galaxies with normal SFRs but low gas content and low depletion times ($lesssim 1$ Gyr), absent from previous surveys. We suggest that the star formation activity of these galaxies has not yet been diminished by their low fraction of cold molecular gas.
Recent molecular line observations with ALMA and NOEMA in several Brightest Cluster Galaxies (BCG) have revealed the large-scale filamentary structure at the center of cool core clusters. These filaments extend over 20-100kpc, they are tightly correlated with ionized gas (H$alpha$, [NII]) emission, and have characteristic shapes: either radial and straight, or also showing a U-turn, like a horse-shoe structure. The kinematics is quite regular and laminar, and the derived infall time is much longer than the free-fall time. The filaments extend up to the radius where the cooling time becomes larger than the infall time. Filaments can be perturbed by the sloshing of the BCG in its cluster, and spectacular cooling wakes have been observed. Filaments tend to occur at the border of cavities driven in the X-ray gas by the AGN radio jets. Observations of cool core clusters support the thermal instability scenario, which accounts for the multiphase medium in the upper atmospheres of BCG, where the right balance between heating and cooling is reached, and a chaotic cold gas accretion occurs. Molecular filaments are also seen associated to ram-pressure stripped spiral galaxies in rich galaxy clusters, and in jet-induced star formation, suggesting a very efficient molecular cloud formation even in hostile cluster environments.
We report the results from a new, highly sensitive ($Delta T_{mb} sim 3 $mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 x 9-pixel grid covering a $1deg$ x $1deg$ patch of sky in the direction of $l = 105deg, b = +2.50deg$ towards the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope (GBT) 1667 MHz OH results with archival CO J=1-0 observations from the Five College Radio Astronomy Observatory (FCRAO) Outer Galaxy Survey within the velocity range of the Perseus Arm at these galactic coordinates. Out of the 81 statistically-independent pointings in our survey area, 86% show detectable OH emission at 1667 MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits below an A$_{rm v}$ of 0.2, but the CO emission does not appear until the volume density exceeds 100-200 cm$^{-3}$. These results demonstrate that a combination of low column density A$_{rm v}$ and low volume density $n_{H}$ can explain the lack of CO emission along sight lines exhibiting OH emission. The 18-cm OH main lines, with their low critical density of $n^{*}$ $ sim 1 $ cm$^{-3}$, are collisionally excited over a large fraction of the quiescent galactic environment and, for observations of sufficient sensitivity, provide an optically-thin radio tracer for diffuse H$_2$.
We have used the ATCA and the SEST to map the large-scale atomic and molecular gas in the nearby Circinus galaxy. The HI mosaic of Circinus exhibits the warps in position angle and inclination revealed in the single-pointing image, both of which appear to settle beyond the inner 30 kpc which was previously imaged. The molecular gas has been mapped in both the CO transitions, where we derive a total molecular gas mass of ~2e9 Mo. Within a radius of 3 kpc, i.e. where CO was clearly detected, the molecular fraction climbs steeply from ~0.7 to unity with proximity to the nucleus. Our HI mosaic gives an atomic gas mass of ~6e9 Mo which is 70% of the fully mapped single dish value. The total neutral gas mass to dynamical mass ratio is therefore 3%, consistent with the SAS3 classification of Circinus. The high (molecular) gas mass fraction found previously, only occurs close to the central ~0.5 kpc and falls to < 10% within and outwith this region, allaying previous concerns regarding the validity of applying the Galactic conversion ratio to Circinus. The rotation curve, as traced by both the HI and CO, exhibits a steep dip at ~1 kpc, the edge of the atomic/molecular ring, within which the star-burst is occurring. We find the atomic and molecular gases to trace different kinematical features and believe that the fastest part of the sub-kpc ring consists overwhelmingly of molecular gas. Beyond the inner kpc, the velocity climbs to settle into a solid body rotation at >10 kpc. Most of the starlight emanates from within this radius and so much of the dynamical mass, which remains climbing to the limit of our data (>50 kpc), must be due to the dark matter halo.
We have recently developed a post-processing framework to estimate the abundance of atomic and molecular hydrogen (HI and H2, respectively) in galaxies in large-volume cosmological simulations. Here we compare the HI and H2 content of IllustrisTNG galaxies to observations. We mostly restrict this comparison to $z approx 0$ and consider six observational metrics: the overall abundance of HI and H2, their mass functions, gas fractions as a function of stellar mass, the correlation between H2 and star formation rate, the spatial distribution of gas, and the correlation between gas content and morphology. We find generally good agreement between simulations and observations, particularly for the gas fractions and the HI mass-size relation. The H2 mass correlates with star formation rate as expected, revealing an almost constant depletion time that evolves up to z = 2 as observed. However, we also discover a number of tensions with varying degrees of significance, including an overestimate of the total neutral gas abundance at z = 0 by about a factor of two and a possible excess of satellites with no or very little neutral gas. These conclusions are robust to the modelling of the HI/H2 transition. In terms of their neutral gas properties, the IllustrisTNG simulations represent an enormous improvement over the original Illustris run. All data used in this paper are publicly available as part of the IllustrisTNG data release.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
