Herschel Virgo Cluster Survey Research Articles

NGC 4370: a case study for testing our ability to infer dust distribution and mass in nearby galaxies

A fraction of the early-type galaxy population hosts a prominent dust lane. Methods to quantify the dust content of these systems based on optical imaging data usually yield dust masses which are an order of magnitude lower than dust masses derived from the observed FIR emission. High-quality optical data from the Next Generation Virgo cluster Survey (NGVS) and FIR/submm observations from the Herschel Virgo Cluster Survey (HeViCS) allow us to revisit previous methods to determine the dust content in galaxies and explore new ones. We aim to derive the dust mass in NGC 4370 from both optical and FIR data, and investigate the need to invoke a putative diffuse dust component. We create color and attenuation maps, which are converted to approximate dust mass maps based on simple dust geometries. Dust masses are also derived from SED fits to FIR/submm observations. Finally, inverse radiative transfer fitting is performed to investigate more complex dust geometries. The empirical methods applied to the optical data yield lower limits of 3.4e5 solar masses, an order of magnitude below the total dust masses derived from SED fitting. In contrast, radiative transfer models yield dust masses which are slightly lower, but fully consistent with the FIR-derived mass. Dust is more likely to be distributed in a ring around the centre of NGC 4370 as opposed to an exponential disc or a simple foreground screen. Moreover, using inverse radiative transfer fitting, we are able to constrain most of the parameters describing these geometries. The resulting dust masses are high enough to account for the dust observed at FIR/submm wavelengths, so that no diffuse dust component needs to be invoked. We furthermore caution for the interpretation of dust masses and optical depths based on optical data alone, using overly simplistic star-dust geometries and the neglect of scattering effects. [ABRIDGED]

TheHerschelVirgo Cluster Survey

To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the far-infrared (FIR) and submillimetre (submm) properties of a sample of star-forming dwarf galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of a total 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than mB = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by β = 1.5, with a median dust temperature Td = 22.4 K. Assuming β = 1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 μm in excess of the modified black-body model. The fraction of galaxies with a submillimetre excess decreases for lower values of β, while a similarly high fraction (54%) is found if a β-free SED modelling is applied. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample that come from environmental effects, we compare the Virgo dwarfs to other Herschel surveys,such as the Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH), the Dwarf Galaxy Survey (DGS), and the HeViCS Bright Galaxy Catalogue (BGC). We explore the relations between stellar mass and Hi fraction, specific star formation rate, dust fraction, gas-to-dust ratio over a wide range of stellar masses (from 107 to 1011 M⊙) for both dwarfs and spirals. Highly Hi-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, to explain the large dust-to-gas mass ratios observed in these systems, we find that the fraction of dust removed has to be less than that of the Hi component. The cluster environment seems to mostly affect the gas component and star formation activity of the dwarfs. Since the Virgo star-forming dwarfs are likely to be crossing the cluster for the first time, a longer timescale might be necessary to strip the more centrally concentrated dust distribution.

TheHerschelVirgo Cluster Survey

We present three independent catalogs of point-sources extracted from SPIRE images at 250, 350, and 500 micron as a part of the Herschel Virgo Cluster Survey (HeViCS). The source positions are determined by estimating the likelihood to be a real source for each peak on the maps and the flux densities are estimated using the sourceExtractorTimeline, a timeline-based point source fitter. Afterwards, each source is subtracted from the maps, removing a Gaussian function in every position with the full width half maximum equal to that estimated in sourceExtractorTimeline. This procedure improves the robustness of our algorithm in terms of source identification. The HeViCS catalogs contain about 52000, 42200, and 18700 sources selected at 250, 350, and 500 micron above 3sigma and are ~ 75%, 62%, and 50% complete at flux densities of 20 mJy at 250, 350, 500 micron, respectively. We then measured source number counts at 250, 350, and 500 micron and we also cross-correlated the catalogs with the Sloan Digital Sky Survey to investigate the redshift distribution of the nearby sources. From this cross-correlation, we select ~2000 sources with reliable fluxes and a high signal-to-noise ratio, finding an average redshift z~0.3+/-0.22. The number counts at 250, 350, and 500 micron show an increase in the slope below 200 mJy, indicating a strong evolution in number of density for galaxies at these fluxes. In general, models tend to overpredict the counts at brighter flux densities, underlying the importance of studying the Rayleigh-Jeans part of the spectral energy distribution to refine the theoretical recipes of the models. Our iterative method for source identification allowed the detection of a family of 500 micron sources that are not foreground objects belonging to Virgo and not found in other catalogs.

A surprising consistency between the far-infrared galaxy luminosity functions of the field and Coma

We present new deep images of the Coma Cluster from the ESA Herschel Space Observatory at wavelengths of 70, 100 and 160 microns, covering an area of 1.75 x 1.0 square degrees encompassing the core and southwest infall region. Our data display an excess of sources at flux densities above 100 mJy compared to blank-field surveys, as expected. We use extensive optical spectroscopy of this region to identify cluster members and hence produce cluster luminosity functions in all three photometric bands. We compare our results to the local field galaxy luminosity function, and the luminosity functions from the Herschel Virgo Cluster Survey (HeViCS). We find consistency between the shapes of the Coma and field galaxy luminosity functions at all three wavelengths, however we do not find the same level of agreement with that of the Virgo Cluster.

The Herschel Fornax Cluster Survey II: FIR properties of optically selected Fornax cluster galaxies

The $Herschel$ Fornax Cluster Survey (HeFoCS) is a deep, far-infrared (FIR) survey of the Fornax cluster. The survey is in 5 $Herschel$ bands (100 - 500 $\mu$m) and covers an area of 16 deg$^2$ centred on NGC1399. This paper presents photometry, detection rates, dust masses and temperatures using an optically selected sample from the Fornax Cluster Catalogue (FCC). Our results are compared with those previously obtained using data from the $Herschel$ Virgo Cluster Survey (HeViCS). In Fornax, we detect 30 of the 237 (13%) optically selected galaxies in at least one $Herschel$ band. The global detection rates are significantly lower than Virgo, reflecting the morphological make up of each cluster - Fornax has a lower fraction of late-type galaxies. For galaxies detected in at least 3 bands we fit a modified blackbody with a $\beta = 2$ emissivity. Detected early-type galaxies (E/S0) have a mean dust mass, temperature, and dust-to-stars ratio of $\log_{10}(<M_{dust}>/\mathrm{M_{\odot}}) = 5.82 \pm 0.20$, $<T_{dust}> = 20.82 \pm 1.77$K, and $\log_{10}(M_{dust}/M_{stars}) = -3.87 \pm 0.28$, respectively. Late-type galaxies (Sa to Sd) have a mean dust mass, temperature, and dust-to-stars ratio of $\log_{10}(<M_{dust}>/\mathrm{M_{\odot}}) = 6.54 \pm 0.19$, $<T_{dust}> = 17.47 \pm 0.97$K, and $\log_{10}(M_{dust}/M_{stars}) = -2.93 \pm 0.09$, respectively. The different cluster environments seem to have had little effect on the FIR properties of the galaxies and so we conclude that any environment dependent evolution, has taken place before the cluster was assembled.

TheHerschelVirgo Cluster Survey

We cross-correlate the Planck Catalogue of Compact Sources (PCCS) with the fully sampled 84 deg2 Herschel Virgo Cluster Survey (HeViCS) fields. We search for and identify the 857 and 545 GHz PCCS sources in the HeViCS fields by studying their FIR/submm and optical counterparts. We find 84 and 48 compact Planck sources in the HeViCS fields at 857 and 545 GHz, respectively. Almost all sources correspond to individual bright Virgo Cluster galaxies. The vast majority of the Planck detected galaxies are late-type spirals, with the Sc class dominating the numbers, while early-type galaxies are virtually absent from the sample, especially at 545 GHz. We compare the HeViCS SPIRE flux densities for the detected galaxies with the four different PCCS flux density estimators and find an excellent correlation with the aperture photometry flux densities, even at the highest flux density levels. We find only seven PCCS sources in the HeViCS fields without a nearby galaxy as obvious counterpart, and conclude that all of these are dominated by Galactic cirrus features or are spurious detections. No Planck sources in the HeViCS fields seem to be associated to high-redshift proto-clusters of dusty galaxies or strongly lensed submm sources. Finally, our study is the first empirical confirmation of the simulation-based estimated completeness of the PCCS, and provides a strong support of the internal PCCS validation procedure.

The Herschel Virgo Cluster Survey – XIV. Transition-type dwarf galaxies in the Virgo cluster

We use dust scaling relations to investigate the hypothesis that Virgo cluster transition-type dwarfs are infalling star-forming field galaxies, which is argued based on their optical features (e.g. disks, spiral arms, bars) and kinematic properties similar to late-type galaxies. After their infall, environmental effects gradually transform them into early-type galaxies through the removal of their interstellar medium and quenching of all star formation activity. In this paper, we aim to verify whether this hypothesis holds using far-infrared diagnostics based on Herschel observations of the Virgo cluster taken as part of the Herschel Virgo Cluster Survey (HeViCS). We select transition-type objects in the nearest cluster, Virgo, based on spectral diagnostics indicative for their residual or ongoing star formation. We detect dust Md ~ 10^{5-6} Msun in 36% of the transition-type dwarfs located on the high end of the stellar mass distribution. This suggests that the dust reservoirs present in non-detections fall just below the Herschel detection limit (< 1.1x10^5 Msun). Dust scaling relations support the hypothesis of a transformation between infalling late-type galaxies to quiescent low-mass spheroids governed by environmental effects, with dust-to-stellar mass fractions for transition-type dwarfs in between values characteristic for late-type objects and the lower dust fractions observed in early-type galaxies. Several transition-type dwarfs demonstrate blue central cores, hinting at the radially outside-in removal of gas and quenching of star formation activity. The fact that dust is also confined to the inner regions suggests that metals are stripped in the outer regions along with the gas. In the scenario of most dust being stripped from the galaxy along with the gas, we argue that... (abridged)

The Herschel Virgo Cluster Survey – XII. FIR properties of optically selected Virgo cluster galaxies

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 $\sim$55 sq. deg. in 5 bands (100-500 \micron), encompassing the areas around the central dominant elliptical galaxies (M87, M86 & M49) and extends as far as the NW cloud, the W cloud and the Southern extension. The survey extends beyond this region with lower sensitivity so that the total area covered is 84 sq. deg. In this paper we describe the data, the data acquisition techniques and present the detection rates of the optically selected Virgo Cluster Catalogue (VCC). We detect 254 (34%) of 750 VCC galaxies found within the survey boundary in at least one band and 171 galaxies are detected in all five bands. For the remainder of the galaxies we have measured strict upper limits for their FIR emission. The population of detected galaxies contains early- as well as late-types although the latter dominate the detection statistics. We have modelled 168 galaxies, showing no evidence of a strong synchrotron component in their FIR spectra, using a single-temperature modified blackbody spectrum with a fixed emissivity index ($\beta = 2$). A study of the $\chi^2$ distribution indicates that this model is not appropriate in all cases, and this is supported by the FIR colours which indicate a spread in $\beta$=1--2. Statistical comparison of the dust mass and temperature distributions from 140 galaxies with $\chi^2_{dof=3} < 7.8$ (95% confidence level) shows that late-types have typically colder, more massive dust reservoirs; the early-type dust masses have a mean of ${\rm log}(<M> / M_{\sun}) = 6.3 \pm 0.3 $, while for late-types ${\rm log}(<M> / M_{\sun}) =7.1 \pm 0.1$... (abridged)

The Herschel Virgo Cluster Survey - VIII. The Bright Galaxy Sample★

We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data that cover the complete survey area (four 4 x 4 deg2 regions). We use these data to measure and compare the global far infrared properties of 78 optically bright galaxies that are selected at 500 \mum and detected in all five far-infrared bands. We show that our measurements and calibration are broadly consistent with previous data obtained by IRAS, ISO, Spitzer and Planck. We use SPIRE and PACS photometry data to produce 100, 160, 250, 350 and 500 \mum cluster luminosity distributions. These luminosity distributions are not power laws, but peaked, with small numbers of both faint and bright galaxies. We measure a cluster 100-500 micron far-infrared luminosity density of 1.6(7.0) \pm 0.2 x 10^9 Lsun/Mpc3. This compares to a cluster 0.4-2.5 \mum optical luminosity density of 5.0(20.0) x 10^9 Lsun/Mpc3, some 3.2(2.9) times larger than the far-infrared. A typical photon originates from an optical depth of 0.4\pm0.1. Most of our sample galaxies are well fitted by a single modified blackbody (beta=2), leading to a mean dust mass of log Mdust = 7.31 Msun and temperature of 20.0 K. We also derive both stellar and atomic hydrogen masses from which we calculate mean values for the stars:gas(atomic) and gas(atomic): dust mass ratios of 15.1 and 58.2 respectively. Using our derived dust, atomic gas and stellar masses we estimate cluster mass densities of 8.6(27.8) x 10^6, 4.6(13.9) x 10^8, 7.8(29.7) x 10^9 Msun/Mpc3, respectively for dust, atomic gas and stars. These values are higher than those derived for field galaxies by factors of 39(126), 6(18) and 34(129) respectively. In the above luminosity/mass densities are given using the whole sample with values in brackets using just those galaxies that lie between 17 and 23 Mpc. We provide a data table of flux densities in all the Herschel bands for all 78 bright Virgo cluster galaxies.

TheHerschelVirgo Cluster Survey

Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster Survey (HeViCS), we investigated the relationship between the metallicity gradients expressed by metal abundances in the gas phase as traced by the chemical composition of HII regions, and in the solid phase, as traced by the dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass ratio for all galaxies observed by HeViCS whose metallicity gradients are available in the literature. They are all late type Sbc galaxies, namely NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on metallicity of the CO-to-H$_2$ conversion factor (\xco), used to transform the $^{12}$CO observations into the amount of molecular hydrogen. We found that in these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive to choice of the \xco\ value, since the molecular gas is the dominant component in the inner parts. We found that for three galaxies of our sample, namely NGC4254, NGC4321, and NGC4501, the slopes of the oxygen and of the dust-to-gas radial gradients agree up to $\sim$0.6-0.7R$_{25}$ using \xco\ values in the range 1/3-1/2 Galactic \xco. For NGC4303 a lower value of \xco$\sim0.1\times$ 10$^{20}$ is necessary. We suggest that such low \xco\ values might be due to a metallicity dependence of \xco (from close to linear for NGC4254, NGC4321, and NGC4501 to superlinear for NGC4303), especially in the radial regions R$_G<$0.6-0.7R$_{25}$ where the molecular gas dominates. On the other hand, the outer regions, where the atomic gas component is dominant, are less affected by the choice of \xco, and thus we cannot put constraints on its value.

The far-infrared view of M87 as seen by the Herschel Space Observatory

AbstractThe origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We observed M87 with PACS and SPIRE as part of the Herschel Virgo Cluster Survey (HeViCS). We compare the new Herschel data with a synchrotron model based on infrared, submm and radio data to investigate the origin of the far-infrared emission. We find that both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87.

TheHerschelVirgo Cluster Survey

We present a resolved dust analysis of three of the largest angular size spiral galaxies, NGC 4501 and NGC 4567/8, in the Herschel Virgo Cluster Survey (HeViCS) Science Demonstration field. Herschel has unprecedented spatial resolution at far-infrared wavelengths and with the PACS and SPIRE instruments samples both sides of the peak in the far infrared spectral energy distribution (SED).We present maps of dust temperature, dust mass, and gas-to-dust ratio, produced by fitting modified black bodies to the SED for each pixel. We find that the distribution of dust temperature in both systems is in the range ~19 - 22 K and peaks away from the centres of the galaxies. The distribution of dust mass in both systems is symmetrical and exhibits a single peak coincident with the galaxy centres. This Letter provides a first insight into the future analysis possible with a large sample of resolved galaxies to be observed by Herschel.

TheHerschelVirgo Cluster Survey

We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data obtained as part of the Science Demonstration Phase (SDP). The data cover a central 4x4 sq deg region of the cluster. We use SPIRE and PACS photometry data to produce 100, 160, 250, 350 and 500 micron luminosity functions (LFs) for optically bright galaxies that are selected at 500 micron and detected in all bands. We compare these LFs with those previously derived using IRAS, BLAST and Herschel-ATLAS data. The Virgo Cluster LFs do not have the large numbers of faint galaxies or examples of very luminous galaxies seen previously in surveys covering less dense environments.