Observations of evolution in the dust-to-metal ratio allow us to constrain the dominant dust processing mechanisms. In this work, we present a study of the dust-to-metal and dust-to-gas ratios in a ...sub-sample of ~500 DustPedia galaxies. Using literature and MUSE emission line fluxes, we derived gas-phase metallicities (oxygen abundances) for over 10 000 individual regions and determine characteristic metallicities for each galaxy. We study how the relative dust, gas, and metal contents of galaxies evolve by using metallicity and gas fraction as proxies for evolutionary state. The global oxygen abundance and nitrogen-to-oxygen ratio are found to increase monotonically as galaxies evolve. Additionally, unevolved galaxies (gas fraction >60%, metallicity 12 + log(O∕H) < 8.2) have dust-to-metal ratios that are about a factor of 2.1 lower (a factor of six lower for galaxies with gas fraction >80%) than the typical dust-to-metal ratio (Md∕MZ ~ 0.214) for more evolved sources. However, for high gas fractions, the scatter is larger due to larger observational uncertainties as well as a potential dependence of the dust grain growth timescale and supernova dust yield on local conditions and star formation histories. We find chemical evolution models with a strong contribution from dust grain growth describe these observations reasonably well. The dust-to-metal ratio is also found to be lower for low stellar masses and high specific star formation rates (with the exception of some sources undergoing a starburst). Finally, the metallicity gradient correlates weakly with the HI-to-stellar mass ratio, the effective radius and the dust-to-stellar mass ratio, but not with stellar mass.
The Herschel Virgo Cluster Survey (HeViCS) is the deepest, confusion-limited survey of the Virgo Cluster at far-infrared (FIR) wavelengths. The entire survey at full depth covers ∼55 deg2 in five ...bands (100-500 μm), encompassing the areas around the central dominant elliptical galaxies (M87, M86 and M49) and extends as far as the NW cloud, the W cloud and the Southern extension. The survey extends beyond this region with lower sensitivity so that the total area covered is 84 deg2. In this paper we describe the data, the data acquisition techniques and present the detection rates of the optically selected Virgo Cluster Catalogue (VCC). We detect 254 (34 per cent) of 750 VCC galaxies found within the survey boundary in at least one band and 171 galaxies are detected in all five bands. For the remainder of the galaxies we have measured strict upper limits for their FIR emission. The population of detected galaxies contains early as well as late types although the latter dominate the detection statistics. We have modelled 168 galaxies, showing no evidence of a strong synchrotron component in their FIR spectra, using a single-temperature modified blackbody spectrum with a fixed emissivity index (β = 2). A study of the χ2 distribution indicates that this model is not appropriate in all cases, and this is supported by the FIR colours which indicate a spread in β = 1-2. Statistical comparison of the dust mass and temperature distributions from 140 galaxies with χ2
d.o.f. = 3 < 7.8 (95 per cent confidence level) shows that late types have typically colder, more massive dust reservoirs; the early-type dust masses have a mean of log〈M〉/M = 6.3 ± 0.3, while for late types log〈M〉/M = 7.1 ± 0.1. The late-type dust temperatures have a mean of 〈T〉 = 19.4 ± 0.2 K, while for the early types, 〈T〉 = 21.1 ± 0.8 K. Late-type galaxies in the cluster exhibit slightly lower dust masses than those in the field, but the cluster environment seems to have little effect on the bulk dust properties of early types. In future papers we will focus more on the scientific analysis of the catalogue (e.g. measuring FIR luminosity functions, dust mass functions and resolved gas and dust properties).
Abstract
We report results from a large molecular line survey of luminous infrared galaxies (LIRGs; L
IR ≳1011L⊙) in the local Universe (z ≤ 0.1), conducted during the last decade with the James ...Clerk Maxwell Telescope and the IRAM 30-m telescope. This work presents the CO and 13CO line data for 36 galaxies, further augmented by multi-J total CO line luminosities available for other infrared (IR) bright galaxies from the literature. This yields a combined sample of N = 70 galaxies with the star formation (SF) powered fraction of their IR luminosities spanning and a wide range of morphologies. Simple comparisons of their available CO spectral line energy distributions (SLEDs) with local ones, as well as radiative transfer models, discern a surprisingly wide range of average interstellar medium (ISM) conditions, with most of the surprises found in the high-excitation regime. These take the form of global CO SLEDs dominated by a very warm (T
kin ≳100 K) and dense (n ≥ 104 cm−3) gas phase, involving galaxy-sized (∼(few) × 109 M⊙) gas mass reservoirs under conditions that are typically found only for ∼(1-3) per cent of mass per typical SF molecular cloud in the Galaxy. Furthermore, some of the highest excitation CO SLEDs are found in ultraluminous infrared galaxies (ULIRGs; L
IR ≥ 1012 L⊙) and surpass even those found solely in compact SF-powered hot spots in Galactic molecular clouds. Strong supersonic turbulence and high cosmic ray energy densities rather than far-ultraviolet/optical photons or supernova remnant induced shocks from individual SF sites can globally warm the large amounts of dense gas found in these merger-driven starbursts and easily power their extraordinary CO line excitation. This exciting possibility can now be systematically investigated with Herschel and the Atacama Large Milimeter Array (ALMA). As expected for an IR-selected (and thus SF rate selected) galaxy sample, only few 'cold' CO SLEDs are found, and for fewer still a cold low/moderate-density and gravitationally bound state (i.e. Galactic type) emerges as the most likely one. The rest remain compatible with a warm and gravitationally unbound low-density phase often found in ULIRGs. Such degeneracies, prominent when only the low-J SLED segment (J = 1-0, 2-1 and 3-2) is available, advise against using its CO line ratios and the so-called X
co = M(H2)/L
co(1-0) factor as SF mode indicators, a practice that may have led to the misclassification of the ISM environments of IR-selected gas-rich discs in the distant Universe. Finally, we expect that the wide range of ISM conditions found among LIRGs will strongly impact the X
co factor, an issue we examine in detail in Paper II.
We report the results of a pilot study with the Expanded Very Large Array (EVLA) of 12CO J= 1-0 emission from four submillimetre-selected galaxies at z= 2.2-2.5, each with an existing detection of ...12CO J= 3-2, one of which comprises two distinct spatial components. Using the EVLA's most compact configuration, we detect strong, broad medians: 990 km s−1 full width at zero intensity; 540 km s−1 full width at half-maximum (FWHM)J= 1-0 line emission from all of our targets - coincident in position and velocity with their J= 3-2 emission. The median linewidth ratio, σ1-0/σ3-2= 1.15 ± 0.06, suggests that the J= 1-0 is more spatially extended than the J= 3-2 emission, a situation confirmed by our maps which reveal velocity structure in several cases and typical sizes of ∼16 kpc FWHM. The median brightness temperature (T
b) ratio is r
3-2/1-0= 0.55 ± 0.05, consistent with local galaxies with L
IR > 1011 L⊙, noting that our value may be biased high because of the J= 3-2 based sample selection. Naively, this suggests gas masses roughly two times higher than estimates made using higher J transitions of CO, with the discrepancy due entirely to the difference in assumed T
b ratio. We also estimate molecular gas masses using the 12CO J= 1-0 line and the observed global T
b ratios, assuming standard underlying T
b ratios for the non-star-forming and star-forming gas phases as well as a limiting star formation efficiency for the latter in all systems, i.e. without calling upon X
CO (≡α). Using this new method, we find a median molecular gas mass of (2.5 ± 0.8) × 1010 M⊙, with a plausible range stretching up to three times higher. Even larger masses cannot be ruled out, but are not favoured by dynamical constraints: the median dynamical mass within R∼ 7 kpc for our sample is (2.3 ± 1.4) × 1011 M⊙ or ∼6 times more massive than UV-selected galaxies at this epoch. We examine the Schmidt-Kennicutt (S-K) relation for all the distant galaxy populations for which CO J= 1-0 or J= 2-1 data are available, finding small systematic differences between galaxy populations. These have previously been interpreted as evidence for different modes of star formation, but we argue that these differences are to be expected, given the still considerable uncertainties, certainly when considering the probable excitation biases due to the molecular lines used, and the possibility of sustained S-K offsets during the evolution of individual gas-rich systems. Finally, we discuss the morass of degeneracies surrounding molecular gas mass estimates, the possibilities for breaking them, and the future prospects for imaging and studying cold, quiescent molecular gas at high redshifts.
Aims. We aim to study the fraction of stellar radiation absorbed by dust, fabs, in 814 galaxies of different morphological types. The targets constitute the vast majority (93%) of the DustPedia ...sample, including almost all large (optical diameter larger than 1′), nearby (v ≤ 3000 km s−1) galaxies observed with the Herschel Space Observatory. Methods. For each object, we modelled the spectral energy distribution from the ultraviolet to the sub-millimetre using the dedicated, aperture-matched DustPedia photometry and the Code Investigating GALaxy Evolution (CIGALE). The value of fabs was obtained from the total luminosity emitted by dust and from the bolometric luminosity, which are estimated by the fit. Results. On average, 19% of the stellar radiation is absorbed by dust in DustPedia galaxies. The fraction rises to 25% if only late-type galaxies are considered. The dependence of fabs on morphology, showing a peak for Sb-Sc galaxies, is weak; it reflects a stronger, yet broad, positive correlation with the bolometric luminosity, which is identified for late-type, disk-dominated, high-specific-star-formation rate, gas-rich objects. We find no variation of fabs with inclination, at odds with radiative transfer models of edge-on galaxies. These results call for a self-consistent modelling of the evolution of the dust mass and geometry along the build-up of the stellar content. We also provide template spectral energy distributions in bins of morphology and luminosity and study the variation of fabs with stellar mass and specific star-formation rate. We confirm that the local Universe is missing the high fabs, luminous and actively star-forming objects necessary to explain the energy budget in observations of the extragalactic background light.
ABSTRACT
The dust mass absorption coefficient, κd is the conversion function used to infer physical dust masses from observations of dust emission. However, it is notoriously poorly constrained, and ...it is highly uncertain how it varies, either between or within galaxies. Here we present the results of a proof-of-concept study, using the DustPedia data for two nearby face-on spiral galaxies M 74 (NGC 628) and M 83 (NGC 5236), to create the first ever maps of κd in galaxies. We determine κd using an empirical method that exploits the fact that the dust-to-metals ratio of the interstellar medium is constrained by direct measurements of the depletion of gas-phase metals. We apply this method pixel-by-pixel within M 74 and M 83, to create maps of κd. We also demonstrate a novel method of producing metallicity maps for galaxies with irregularly sampled measurements, using the machine learning technique of Gaussian process regression. We find strong evidence for significant variation in κd. We find values of κd at 500 $\mu$m spanning the range 0.11–0.25 ${\rm m^{2}\, kg^{-1}}$ in M 74, and 0.15–0.80 ${\rm m^{2}\, kg^{-1}}$ in M 83. Surprisingly, we find that κd shows a distinct inverse correlation with the local density of the interstellar medium. This inverse correlation is the opposite of what is predicted by standard dust models. However, we find this relationship to be robust against a large range of changes to our method – only the adoption of unphysical or highly unusual assumptions would be able to suppress it.
We use approximately 1000 X-ray sources in the COSMOS-Legacy survey and study the position of the AGN relative to the star forming main sequence (MS). We also construct a galaxy (non-AGN) reference ...sample that includes about 90 000 sources. We apply the same photometric selection criteria to both datasets and construct their spectral energy distributions (SEDs) using optical to far-infrared photometry compiled by the HELP project. We perform SED fitting using the X-CIGALE algorithm and the same parametric grid for both datasets in order to measure the star formation rate (SFR) and stellar mass of the sources. The mass completeness of the data is calculated at different redshift intervals and is applied to both samples. We define our own MS based on the distributions of the specific SFR at different redshift ranges and exclude quiescent galaxies from our analysis. These allow us to compare the SFR of the two populations in a uniform manner, minimising systematic errors and selection effects. Our results show that at low to moderate X-ray luminosities, AGN tend to have lower or at most equal SFRs compared to non-AGN systems with similar stellar mass and redshift. At higher (
L
X, 2 − 10 keV
> 2 − 3 × 10
44
erg s
−1
), we observe an increase in the SFR of AGN for systems that have 10.5 < log
M
*
(
M
⊙
) < 11.5.
Aims. We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim ...is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies. Methods. We used Herschel observations and atomic and molecular gas masses to estimate ϵ(250 μm), the disc-averaged dust emissivity at 250 μm, and from this, the absorption cross section per H atom σ(250 μm) and per dust mass κ(250 μm). The emissivity ϵ(250 μm) requires one assumption, which is the CO-to-H2 conversion factor, and the dust temperature is additionally required for σ(250 μm); yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required for κ(250 μm). Results. We find ϵ(250 μm) = 0.82 ± 0.07 MJy sr−1 (1020 H cm−2)−1 for galaxies with 4 < F(250 μm)/F(500 μm) < 5. This depends only weakly on the adopted CO-to-H2 conversion factor. The value is almost the same as that for the Milky Way at the same colour ratio. Instead, for F(250 μm)/F(500 μm) > 6, ϵ(250 μm) is lower than predicted by its dependence on the heating conditions. The reduction suggests a variation in dust emission properties for spirals of earlier type, higher metallicity, and with a higher fraction of molecular gas. When the standard emission properties of Galactic cirrus are used for these galaxies, their dust masses might be underestimated by up to a factor of two. Values for σ(250 μm) and κ(250 μm) at the Milky Way metallicity are also close to those of the cirrus. Mild trends of the absorption cross sections with metallicity are found, although the results depend on the assumptions made.
Aims.
The general consensus is that late-type galaxies undergo intense star-formation, activity while early-type galaxies are mostly inactive. We question this general rule and investigate the ...existence of star-forming early-type and quiescent late-type galaxies in the local Universe. By computing the physical properties of these galaxies and by using information on their structural properties as well as the density of their local environment, we seek to understand the differences from their ‘typical’ counterparts.
Methods.
We made use of the multi-wavelength photometric data (from the ultraviolet to the sub-millimetre), for 2209 morphologically classified galaxies in the Galaxy And Mass Assembly survey. Furthermore, we separated the galaxies into subsets of star-forming and quiescent based on their dominant ionising process, making use of established criteria based on the
W
H
α
width and the N
II
/H
α
ratio. Taking advantage of the spectral energy distribution fitting code
CIGALE
, we derived galaxy properties, such as the stellar mass, dust mass, and star-formation rate, and we also estimated the unattenuated and the dust-absorbed stellar emission, for both the young (≤200 Myr) and old (> 200 Myr) stellar populations.
Results.
We find that about 47% of E/S0 galaxies in our sample show ongoing star-formation activity and 8% of late-type galaxies are quiescent. The star-forming elliptical galaxies, together with the little blue spheroids, constitute a population that follows the star-forming main sequence of spiral galaxies very well. The fraction of the luminosity originating from young stars in the star-forming early-type galaxies is quite substantial (∼25%) and similar to that of the star-forming late-type galaxies. The stellar luminosity absorbed by the dust (and used to heat the dust grains) is highest in star-forming E/S0 galaxies (an average of 35%) followed by star-forming Sa-Scd galaxies (27%) with this fraction becoming significantly smaller for their quiescent analogues (6% and 16%, for E/S0 and Sa-Scd, respectively). Star-forming and quiescent E/S0 galaxies donate quite different fractions of their young stellar luminosities to heat up the dust grains (74% and 36%, respectively), while these fractions are very similar for star-forming and quiescent Sa-Scd galaxies (59% and 60%, respectively). Investigating possible differences between star-forming and quiescent galaxies, we find that the intrinsic (unattenuated) shape of the SED of the star-forming galaxies is, on average, very similar for all morphological types. Concerning their structural parameters, quiescent galaxies tend to show larger values of the
r
-band Sérsic index and larger effective radii (compared to star-forming galaxies). Finally, we find that star-forming galaxies preferably reside in lower density environments compared to the quiescent ones, which exhibit a higher percentage of sources being members of groups.
We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk 231. In total 25 lines are detected, including CO J = 5–4 through J = 13–12, 7 rotational lines of ...H2O, 3 of OH+ and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J = 8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J = 8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk 231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk 231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J = 8. X-rays from the accreting supermassive black hole in Mrk 231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk 231. The extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of X-ray driven excitation and chemistry in this region.
PDF
