We investigate the connection between dust and gas in the nearby edge-on spiral galaxy NGC 891, a target of the Very Nearby Galaxies Survey. High resolution Herschel PACS and SPIRE 70, 100, 160, 250, ...350, and 500 μm images are combined with JCMT SCUBA 850 μm observations to trace the far-infrared/submillimetre spectral energy distribution (SED). Maps of the Hi 21 cm line and CO(J = 3−2) emission trace the atomic and molecular hydrogen gas, respectively. We fit one-component modified blackbody models to the integrated SED, finding a global dust mass of (8.5 ± 2.0) × 107 M⊙ and an average temperature of 23 ± 2 K, consistent with results from previous far-infrared experiments. We also fit one-component modified blackbody models to pixel-by-pixel SEDs to produce maps of the dust mass and temperature. The dust mass distribution correlates with the total stellar population as traced by the 3.6 μm emission. The derived dust temperature, which ranges from approximately 17 to 24 K, is found to correlate with the 24 μm emission. Allowing the dust emissivity index to vary, we find an average value of β = 1.9 ± 0.3. We confirm an inverse relation between the dust emissivity spectral index and dust temperature, but do not observe any variation of this relationship with vertical height from the mid-plane of the disc. A comparison of the dust properties with the gaseous components of the ISM reveals strong spatial correlations between the surface mass densities of dust (Σdust) and the molecular hydrogen (ΣH2) and total gas surface densities (Σgas). These observations reveal the presence of regions of dense, cold dust that are coincident with peaks in the gas distribution and are associated with a molecular ring. Furthermore, the observed asymmetries in the dust temperature, the H2-to-dust ratio and the total gas-to-dust ratio hint that an enhancement in the star formation rate may be the result of larger quantities of molecular gas available to fuel star formation in the NE compared to the SW. Whilst the asymmetry likely arises from dust obscuration due to the geometry of the line-of-sight projection of the spiral arms, we cannot exclude that there is also an enhancement in the star formation rate in the NE part of the disc.
With the newly available photometric images at 250 and 500 mu m from the Herschel Space Observatory, we study quantitative correlations over a sub-kiloparsec scale among three distinct emission ...components in the interstellar medium of the nearby spiral galaxy M81 (NGC 3031): (1) I sub(8) or I sub(24), the surface brightness of the mid-infrared emission observed in the Spitzer Space Telescope 8 or 24 mu m band, with I sub(8) and I sub(24) being dominated by the emissions from polycyclic aromatic hydrocarbons (PAHs) and very small grains (VSGs) of dust, respectively; (2) I sub(500), that of the cold dust continuum emission in the Herschel Space Observatory 500 mu m band, dominated by the emission from large dust grains heated by evolved stars; and (3) I sub(H alpha ), a nominal surface brightness of the H alpha line emission, from gas ionized by newly formed massive stars. The results from our correlation study, free from any assumption on or modeling of dust emissivity law or dust temperatures, present solid evidence for significant heating of PAHs and VSGs by evolved stars. In the case of M 81, about 67% (48%) of the 8 mu m (24 mu m) emission derives its heating from evolved stars, with the remainder attributed to radiation heating associated with ionizing stars.
We present an integrated photometric spectral energy distribution (SED) of the Magellanic-type galaxy NGC 4449 from the far-ultraviolet (UV) to the submillimetre, including new observations acquired ...by the Herschel Space Observatory. We include integrated UV photometry from the Swift Ultraviolet and Optical Telescope using a measurement technique which is appropriate for extended sources with coincidence loss. In this paper, we examine the available multiwavelength data to infer a range of ages, metallicities and star formation rates for the underlying stellar populations, as well as the composition and the total mass of dust in NGC 4449. Our analysis of the global optical spectrum of NGC 4449 fitted using the spectral fitting code starlight suggests that the majority of stellar mass resides in old ( 1 Gyr old) and metal-poor (Z/Z ∼ 0.2) populations, with the first onset of star formation activity deduced to have taken place at an early epoch, approximately 12 Gyr ago. A simple chemical evolution model, suitable for a galaxy continuously forming stars, suggests a ratio of carbon to silicate dust mass comparable to that of the Large Magellanic Cloud over the inferred time-scales. We present an iterative scheme, which allows us to build an in-depth and multicomponent representation of NGC 4449 'bottom-up', taking advantage of the broad capabilities of the photoionization and radiative transfer code mocassin (MOnte CArlo SimulationS of Ionized Nebulae). We fit the observed SED, the global ionization structure and the emission line intensities, and infer a recent star formation rate of 0.4 M yr− 1 and a total stellar mass of 1 × 109 M emitting with a bolometric luminosity of 5.7 × 109 L. Our fits yield a total dust mass of 2.9 ± 0.5 × 106 M including 2 per cent attributed to polycyclic aromatic hydrocarbons. We deduce a dust to gas mass ratio of 1/190 within the modelled region. While we do not consider possible additional contributions from even colder dust, we note that including the extended H i envelope and the molecular gas is likely to bring the ratio down to as low as ∼1/800.
The Herschel Virgo Cluster Survey Grossi, M; Hunt, L K; Madden, S C ...
Astronomy and astrophysics (Berlin),
02/2015, Letnik:
574
Journal Article
Recenzirano
Odprti dostop
The aim of this study is to assess the effects of the cluster environment on the different components of the interstellar medium, we analyze the far-infrared (FIR) and sub-millimetre (sub-mm) ...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. 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.
Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to ...its CO and H I emission. Depending on the dust emissivity, the total dust mass is 2-5 x 10 super(6) M sub(middot in circle). While the neutral gas-to-dust mass ratio is extremely low (< 12-30), including the ionized gas traced by CII emission raises this limit to <39-100. The dust emission follows a similar r super(1/4) profile to the stellar light and the dust to stellar mass ratio is toward the high end of what is found in nearby elliptical galaxies. We suggest that NGC 4125 is currently in an unusual phase where evolved stars produced in a merger-triggered burst of star formation are pumping large amounts of gas and dust into the interstellar medium. In this scenario, the low neutral gas-to-dust mass ratio is explained by the gas being heated to temperatures > or =, slant10 super(4) K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.
Far-reaching dust distribution in galaxy discs Smith, Matthew W. L; Eales, Stephen A; De Looze, Ilse ...
Monthly notices of the Royal Astronomical Society,
10/2016, Letnik:
462, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In most studies of dust in galaxies, dust is only detected from its emission to approximately the optical radius of the galaxy. By combining the signal of 110 spiral galaxies observed as part of the ...Herschel Reference Survey, we are able to improve our sensitivity by an order of magnitude over that for a single object. Here we report the direct detection of dust from its emission that extends out to at least twice the optical radius. We find that the distribution of dust is consistent with an exponential at all radii with a gradient of ∼−1.7 dex
$R_{25}^{-1}$
. Our dust temperature declines linearly from ∼25 K in the centre to 15 K at R
25 from where it remains constant out to ∼2.0 R
25. The surface density of dust declines with radius at a similar rate to the surface density of stars but more slowly than the surface density of the star-formation rate. Studies based on dust extinction and reddening of high-redshift quasars have concluded that there are substantial amounts of dust in intergalactic space. By combining our results with the number counts and angular correlation function from the SDSS, we show that with Milky Way-type dust we can explain the reddening of the quasars by the dust within galactic discs alone. Given the uncertainties in the properties of any intergalactic dust, we cannot rule out its existence, but our results show that statistical investigations of the dust in galactic haloes that use the reddening of high-redshift objects must take account of the dust in galactic discs.
For this study, we combine two samples of local galaxies observed with Herschel: the Dwarf Galaxy Survey (DGS, Madden et al., 2013PASP..125..600M) and the Key Insights on Nearby Galaxies: a ...Far-Infrared Survey with Herschel (KINGFISH, Kennicutt et al., 2011PASP..123.1347K). (7 data files).
How galaxies turn metals into dust and gas and eventual star formation is the crux to understanding the evolution of the cosmos. We find that the lowest metallicity star forming dwarf galaxies have ...much lower dust abundance than previously expected, compared to their total metals and gas reservoirs. Little dust, and challenging CO observations and relatively bright far-infrared fine structure lines, such as 158 μm CII and 88 μm OIII reveal the structure of the interstellar medium to be very porous to UV radiation, leaving dwarf galaxies with a significant filling factor of ionized gas, and photo dissociated envelopes. The infrared fine structure lines together provide a tool to quantify the important reservoir of molecular gas in dwarf galaxies not traced by CO: the CO dark gas component.
PDF
