We study the properties of the cold gas component of the interstellar medium of the Herschel Reference Survey, a complete volume-limited (15 <, ~ D <, ~ 25 Mpc), K-band-selected sample of galaxies ...spanning a wide range in morphological type (from ellipticals to dwarf irregulars) and stellar mass (10 super(9) <, ~ M sub(star) <, ~ 10 super(11) M sub(middot in circle)). The multifrequency data in our hands are used to trace the molecular gas mass distribution and the main scaling relations of the sample, which put strong constraints on galaxy formation simulations. We extend the main scaling relations concerning the total and the molecular gas component determined for massive galaxies (M sub(star) > ~ 10 super(10) M sub(middot in circle)) from the COLD GASS survey down to stellar masses M sub(star) = 10 super(9) M sub(middot in circle). As scaling variables we use the total stellar mass M sub(star), the stellar surface density mu sub(star), the specific star formation rate SSFR, and the metallicity of the target galaxies. By comparing molecular gas masses determined using a constant or a luminosity dependent X sub(CO) conversion factor, we estimate the robustness of these scaling relations on the very uncertain assumptions used to transform CO line intensities into molecular gas masses. The molecular gas distribution of a K-band-selected sample is significantly different from that of a far-infrared-selected sample since it includes a significantly smaller number of objects with M(H sub(2)) <, ~ 6 x 10 super(9) M sub(middot in circle). In spiral galaxies the molecular gas phase is only 25-30% of the atomic gas. The analysis also indicates that the slope of the main scaling relations depends on the adopted conversion factor. Among the sampled relations, all those concerning M(gas)/M sub(star) are statistically significant and show little variation with X sub(CO). We observe a significant correlation between M(H sub(2))/M sub(star) and SSFR, M(H sub(2))/M(HI ) and mu sub(star), M(H sub(2))/M(HI ) and 12 +log (O/H), regardless of the adopted X sub(CO). The total and molecular gas consumption timescales are anticorrelated with the specific star formation rate. The comparison of HRS and COLD GASS data indicates that some of the observed scaling relations are nonlinear.
The Herschel Reference Survey is a complete volume-limited, K-band-selected sample of nearby objects including Virgo cluster and isolated objects. Using a recent compilation of HI and CO data for ...this sample we study the effects of the cluster environment on the molecular gas content of spiral galaxies. With the subsample of unperturbed field galaxies, we first identify the stellar mass as the scaling variable that traces the total molecular gas mass of galaxies better. We show that, on average, HI-deficient galaxies are significantly offset (4sigma) from the M(H sub(2)) vs. M sub(star) relation for HI-normal galaxies. We use the M(H sub(2)) vs. M sub(star) scaling relation to define the H sub(2)-deficiency parameter as the difference, on logarithmic scale, between the expected and observed molecular gas mass for a galaxy of given stellar mass. The H sub(2)-deficiency parameter shows a weak and scattered relation with the HI-deficiency parameter, here taken as a proxy for galaxy interactions with the surrounding cluster environment. We also show that, as for the atomic gas, the extent of the molecular disc decreases with increasing HI-deficiency. All together, these results show that cluster galaxies have, on average, a lower molecular gas content than similar objects in the field. Our analysis indicates that ram pressure stripping is the physical process responsible for this molecular gas deficiency. The slope of the H sub(2) - def vs. HI - def relation is less than unity, while the D(HI)/D(i) vs. HI - def relation is steeper than the D(CO)/D(i) vs. HI - def relation, thereby indicating that the molecular gas is removed less efficiently than the atomic gas. This result can be understood if the atomic gas is distributed on a relatively flat disc that is more extended than the stellar disc. It is thus less anchored to the gravitational potential well of the galaxy than the molecular gas phase, which is distributed on an exponential disc with a scalelength r sub(CO) Asymptotically = to 0.2r sub(24.5) (g). There is a clear trend between the NUV-i colour index, which is a proxy for the specific star formation activity, and the H sub(2)-deficiency parameter, which suggests that molecular gas removal quenches the activity of star formation. This causes galaxies migrate from the blue cloud to the green valley and, eventually, to the red sequence. The total gas-consumption timescale of gas deficient cluster galaxies is comparable to that of isolated, unperturbed systems. The total gas depletion timescale determined by considering the recycled fraction is T sub(gas,R) Asymptotically = to 3.0-3.3 Gyr, which is significantly larger than the typical timescale for total gas removal in a ram pressure stripping process, indicated by recent hydrodynamical simulations to be T sub(RP)Asympt otically = to 1.5 Gyr. The comparison of these timescales suggests that ram pressure, rather than a simple stop of the infall of pristine gas from the halo, will be the dominant process driving the future evolution of these cluster galaxies.
With the aim of quantifying the contribution of the environment on the evolution of galaxies at z = 0 we have used the DR7 catalogue of the Sloan Digital Sky Survey (SDSS) to reconstruct the 3-D ...distribution of 4132 galaxies in 420 square degrees of the Coma supercluster, containing two rich clusters (Coma and A1367), several groups, and many filamentary structures belonging to the “Great Wall”, at the approximate distance of 100 Mpc. At this distance the galaxy census is complete to Mi = –17.5 mag, i.e. ~4 mag fainter than M*. The morphological classification of galaxies into early- (ellipticals) and late-types (spirals) was carried out by inspection of individual SDSS images and spectra. The density around each galaxy was determined in cylinders of 1 Mpc radius and 1000 km s-1 half length. The color-luminosity relation was derived for galaxies in bins morphological type and in four thresholds of galaxy density-contrast, ranging from δ1,1000 ≤ 0 (UL = the cosmic web); 0 < δ1,1000 ≤ 4 (L = the loose groups); 4 < δ1,1000 ≤ 20 (H = the large groups and the cluster's outskirts) and δ1,1000 > 20 (UH = the cluster's cores). The fraction of early-type galaxies increases with the log of the over-density. A well defined “red sequence” composed of early-type galaxies exists in all environments at high luminosity, but it lacks of low luminosity (dwarf) galaxies in the lowest density environment. Conversely low luminosity isolated galaxies are predominantly of late-type. In other words the low luminosity end of the distribution is dominated by red dE galaxies in clusters and groups and by dwarf blue amorphous systems in the lowest density regions. At z = 0 we find evidence for strong evolution induced by the environment (Nurture). Transformations take place mostly at low luminosity when star forming dwarf galaxies inhabiting low density environments migrate into amorphous passive dwarf ellipticals in their infall into denser regions. The mechanism involves suppression of the star formation due to gas stripping, without significant mass growth, as proposed by Boselli et al. (2008a, ApJ, 674, 742). This process is more efficient and fast in ambients of increasing density. In the highest density environments (around clusters) the truncation of the star formation happens fast enough (few 100 Myr) to produce the signature of post-star-burst in galaxy spectra. PSB galaxies, that are in fact found significantly clustered around the largest dynamical units, represent the remnants of star forming isolated galaxies that had their star formation violently suppressed during their infall in clusters in the last 0.5–1.5 Gyrs, and the progenitors of future dEs.
The Herschel Dwarf Galaxy Survey Cormier, D; Madden, S C; Lebouteiller, V ...
Astronomy and astrophysics (Berlin),
06/2015, Letnik:
578
Journal Article
Recenzirano
Odprti dostop
The far-infrared (FIR) lines are important tracers of the cooling and physical conditions of the interstellar medium (ISM) and are rapidly becoming workhorse diagnostics for galaxies throughout the ...universe. Our goal is to explain the main differences and trends observed in the FIR line emission of dwarf galaxies compared to more metal-rich alaxies, and how this translates in ISM properties. We present Herschel/PACS spectroscopic observations of the CII 157 mum, OI 63 and 145 mum, OIII 88 mum, NII 122 and 205 mum, and NIII 57 mum fine-structure cooling lines in a sample of 48 low-metallicity star-forming galaxies of the guaranteed time key program Dwarf Galaxy Survey. We correlate PACS line ratios and line-to-LTIR ratios with LTIR, LTIR/LB, metallicity, and FIR color, and interpret the observed trends in terms of ISM conditions and phase filling factors with Cloudy radiative transfer models.
Aims. In this work, we aim to provide a consistent analysis of the dust properties from metal-poor to metal-rich environments by linking them to fundamental galactic parameters. Methods. We consider ...two samples of galaxies: the Dwarf Galaxy Survey (DGS) and the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel (KINGFISH), totalling 109 galaxies, spanning almost 2 dex in metallicity. We collect infrared (IR) to submillimetre (submm) data for both samples and present the complete data set for the DGS sample. We model the observed spectral energy distributions (SED) with a physically-motivated dust model to access the dust properties: dust mass, total-IR luminosity, polycyclic aromatic hydrocarbon (PAH) mass fraction, dust temperature distribution, and dust-to-stellar mass ratio. Results. Using a different SED model (modified black body), different dust composition (amorphous carbon in lieu of graphite), or a different wavelength coverage at submm wavelengths results in differences in the dust mass estimate of a factor two to three, showing that this parameter is subject to non-negligible systematic modelling uncertainties. We find half as much dust with the amorphous carbon dust composition. For eight galaxies in our sample, we find a rather small excess at 500 μm (≤1.5σ). We find that the dust SED of low-metallicity galaxies is broader and peaks at shorter wavelengths compared to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The PAH mass fraction and dust temperature distribution are found to be driven mostly by the specific star formation rate, sSFR, with secondary effects from metallicity. The correlations between metallicity and dust mass or total-IR luminosity are direct consequences of the stellar mass-metallicity relation. The dust-to-stellar mass ratios of metal-rich sources follow the well-studied trend of decreasing ratio for decreasing sSFR. The relation is more complex for low-metallicity galaxies with high sSFR, and depends on the chemical evolutionary stage of the source (i.e. gas-to-dust mass ratio). Dust growth processes in the ISM play a key role in the dust mass build-up with respect to the stellar content at high sSFR and low metallicity. Conclusions. We conclude that the evolution of the dust properties from metal-poor to metal-rich galaxies derives from a complex interplay between star formation activity, stellar mass, and metallicity.
Aims. The goal of this paper is to analyse the behaviour of the gas-to-dust mass ratio (G/D) of local Universe galaxies over a wide metallicity range. We especially focus on the low-metallicity part ...of the G/D vs metallicity relation and investigate several explanations for the observed relation and scatter. Methods. We assembled a total of 126 galaxies, covering a 2 dex metallicity range and with 30% of the sample with 12 + log(O/H)≤ 8.0. We homogeneously determined the dust masses with a semi-empirical dust model including submm constraints. The atomic and molecular gas masses have been compiled from the literature. We used two XCO scenarios to estimate the molecular gas mass: the Galactic conversion factor, XCO,MW, and a XCO that depends on the metallicity XCO,Z (∝Z-2). We modelled the observed trend of the G/D with metallicity using two simple power laws (slope of –1 and free) and a broken power law. Correlations with morphological type, stellar masses, star formation rates, and specific star formation rates are also discussed. We then compared the observed evolution of the G/D with predictions from several chemical evolution models and explored different physical explanations for the observed scatter in the G/D values. Results. We find that out of the five tested galactic parameters, metallicity is the main physical property of the galaxy driving the observed G/D. The G/D versus metallicity relation cannot be represented by a single power law with a slope of –1 over the whole metallicity range. The observed trend is steeper for metallicities lower than ~8.0. A large scatter is observed in the G/D values for a given metallicity: in metallicity bins of ~0.1 dex, the dispersion around the mean value is ~0.37 dex. On average, the broken power law reproduces the observed G/D best compared to the two power laws (slope of –1 or free) and provides estimates of the G/D that are accurate to a factor of 1.6. The good agreement of observed values of the G/D and its scatter with respect to metallicity with the predicted values of the three tested chemical evolution models allows us to infer that the scatter in the relation is intrinsic to galactic properties, reflecting the different star formation histories, dust destruction efficiencies, dust grain size distributions, and chemical compositions across the sample. Conclusions. Our results show that the chemical evolution of low-metallicity galaxies, traced by their G/D, strongly depends on their local internal conditions and individual histories. The large scatter in the observed G/D at a given metallicity reflects the impact of various processes occurring during the evolution of a galaxy. Despite the numerous degeneracies affecting them, disentangling these various processes is now the next step.
We investigate the timescale over which the infrared (IR) luminosity decreases after a complete and rapid quenching of star formation using observations of local and high-redshift galaxies. From ...spectral energy distribution modelling, we derive the time since quenching of a subsample of 14 galaxies from the
Herschel
Reference Survey that suffer from ram-pressure stripping due to the environment of the Virgo cluster and of a subsample of 7 rapidly quenched COSMOS galaxies selected through a state-of-the-art statistical method already tested on the determination of galaxy star formation history (SFH). Three out of the seven COSMOS galaxies have an optical spectrum with no emission line, confirming their quenched nature. We obtained the present physical properties of the combined sample (local plus high-redshift) from the long-term SFH properties, as well as the past
L
IR
of these galaxies just before their quenching. We show that this past
L
IR
is consistent with the
L
IR
of reference samples of normally star-forming galaxies with same stellar mass and redshift as each of our quenched galaxies. We put constraints on the present to past IR luminosity ratio as a function of quenching time. The two samples probe different dynamical ranges in terms of quenching age with the HRS galaxies exhibiting longer timescales (0.2–3 Gyr) compared to the COSMOS ones (< 100 Myr). Assuming an exponential decrease in the
L
IR
after quenching, the COSMOS quenched galaxies are consistent with short e-folding times of less than a couple of hundred million years, while the properties of the HRS quenched galaxies are compatible with larger timescales of several hundred million years. For the HRS sample, this result is consistent with the known quenching mechanism that affected them, namely ram pressure stripping due to the environment. For the COSMOS sample, different quenching processes are acting on short to intermediate timescales. Processes such as galaxy mergers, disk instabilities, and environmental effects can produce such strong star formation variability.
We present measurements of the auto- and cross-frequency power spectra of the cosmic infrared background (CIB) at 250, 350, and 500 mu m (1200, 860, and 600 GHz) from observations totaling ~70 deg ...sub(2) made with the SPIRE instrument aboard the Herschel Space Observatory. We measure a fractional anisotropy delta I/I = 14% + or - 4% , detecting signatures arising from the clustering of dusty star-forming galaxies in both the linear (2-halo) and nonlinear (1-halo) regimes; and that the transition from the 2- to 1-halo terms, below which power originates predominantly from multiple galaxies within dark matter halos, occurs at k sub(theta) ~ 0.10-0.12 aremin super(-1) (l ~ 2160-2380), from 250 to 500 mu m. We measure the cross-correlation power spectra between bands, finding that bands which are farthest apart are the least correlated, as well as hints of a reduction in the correlation between bands when resolved sources are more aggressively masked.
WALLABY – an SKA Pathfinder H i survey Koribalski, Bärbel S.; Staveley-Smith, L.; Westmeier, T. ...
Astrophysics and space science,
07/2020, Letnik:
365, Številka:
7
Journal Article
Recenzirano
The Widefield ASKAP L-band Legacy All-sky Blind surveY (
wallaby
) is a next-generation survey of neutral hydrogen (H
i
) in the Local Universe. It uses the widefield, high-resolution capability of ...the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of
36
×
12
-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia.
wallaby
aims to survey three-quarters of the sky (
−
90
∘
<
δ
<
+
30
∘
) to a redshift of
z
≲
0.26
, and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam
−1
per 4 km s
−1
channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five,
wallaby
is expected to detect around half a million galaxies with a mean redshift of
z
∼
0.05
(∼200 Mpc). The scientific goals of
wallaby
include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H
i
properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H
i
surveys. Combined with existing and new multi-wavelength sky surveys,
wallaby
will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the
wallaby
pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).
Multi-Unit Spectroscopic Explorer (MUSE) observations of the cluster of galaxies CGr32 (M200 ≃ 2 × 1014 M⊙) at z = 0.73 reveal the presence of two massive star-forming galaxies with extended tails of ...diffuse gas detected in the O IIλλ3727–3729 Å emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10−18 erg s−1 cm−2 arcsec−2, extend up to ≃100 kpc (projected distance) from the galaxy discs, and are not associated with any stellar component. All this observational evidence suggests that the gas was removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe was only half its present age. The density of the gas derived using the observed O IIλ3729/O IIλ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail.
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