High-resolution radiative transfer modelling of M33 Williams, Thomas G; Baes, Maarten; De Looze, Ilse ...
Monthly notices of the Royal Astronomical Society,
08/2019, Letnik:
487, Številka:
2
Journal Article
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ABSTRACT
In this work, we characterize the contributions from both ongoing star formation and the ambient radiation field in Local Group galaxy M33, as well as estimate the scale of the local ...dust-energy balance (i.e. the scale at which the dust is re-emitting starlight generated in that same region) in this galaxy through high-resolution radiative transfer (RT) modelling, with defined stellar and dust geometries. We have characterized the spectral energy distribution (SED) of M33 from UV to sub-mm wavelengths, at a spatial scale of 100 pc. We constructed input maps of the various stellar and dust geometries for use in the RT modelling. By modifying our dust mix (fewer very small carbon grains and a lower silicate-to-carbon ratio as compared to the Milky Way), we can much better fit the sub-mm dust continuum. Using this new dust composition, we find that we are able to well reproduce the observed SED of M33 using our adopted model. In terms of stellar attenuation by dust, we find a reasonably strong, broad UV bump, as well as significant systematic differences in the amount of dust attenuation when compared to standard SED modelling. We also find discrepancies in the residuals of the spiral arms versus the diffuse interstellar medium (ISM), indicating a difference in properties between these two regimes. The dust emission is dominated by heating due to the young stellar populations at all wavelengths (∼80 per cent at 10 $\mu$m to ∼50 per cent at 1 mm). We find that the local dust-energy balance is restored at spatial scales greater than around 1.5 kpc.
Context.
M 33 is a gas rich spiral galaxy of the Local Group. Its vicinity allows us to study its interstellar medium (ISM) on linear scales corresponding to the sizes of individual giant molecular ...clouds.
Aims.
We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum.
Methods.
We mapped the emission of gas and dust in M 33 using the far-infrared lines of C
II
and O
I
(63
μ
m) and the total infrared continuum. The line maps were observed with the PACS spectrometer on board the
Herschel
Space Observatory. These maps have 50 pc resolution and form a ∼370 pc wide stripe along its major axis covering the sites of bright H
II
regions, but also more quiescent arm and inter-arm regions from the southern arm at 2 kpc galacto-centric distance to the south out to 5.7 kpc distance to the north. Full-galaxy maps of the continuum emission at 24
μ
m from
Spitzer
/MIPS, and at 70
μ
m, 100
μ
m, and 160
μ
m from
Herschel
/PACS were combined to obtain a map of the TIR.
Results.
TIR and C
II
intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of
G
0, obs
∼ 2 to 200 in units of the average Galactic radiation field. The binned C
II
/TIR ratio drops with rising TIR, with large, but decreasing scatter. The contribution of the cold neutral medium to the C
II
emission, as estimated from VLA H
I
data, is on average only 10%. Fits of modified black bodies to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the O
I
data before comparing it with models of photon dominated regions. Most of the ratios of C
II
/O
I
and (C
II
+O
I
)/TIR are consistent with two model solutions. The median ratios are consistent with one solution at
n
∼ 2 × 10
2
cm
−3
,
G
0
∼ 60, and a second low-FUV solution at
n
∼ 10
4
cm
−3
,
G
0
∼ 1.5.
Conclusions.
The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ∼1. A fraction of the gas may, however, be represented by the second solution.
Context. M 33 is a gas rich spiral galaxy of the Local Group. Its vicinity allows us to study its interstellar medium (ISM) on linear scales corresponding to the sizes of individual giant molecular ...clouds. Aims. We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum. Methods. We mapped the emission of gas and dust in M 33 using the far-infrared lines of C II and O I(63 μm) and the total infrared continuum. The line maps were observed with the PACS spectrometer on board the Herschel Space Observatory. These maps have 50 pc resolution and form a ∼370 pc wide stripe along its major axis covering the sites of bright H II regions, but also more quiescent arm and inter-arm regions from the southern arm at 2 kpc galacto-centric distance to the south out to 5.7 kpc distance to the north. Full-galaxy maps of the continuum emission at 24 μm from Spitzer/MIPS, and at 70 μm, 100 μm, and 160 μm from Herschel/PACS were combined to obtain a map of the TIR. Results. TIR and C II intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of G0, obs ∼ 2 to 200 in units of the average Galactic radiation field. The binned C II/TIR ratio drops with rising TIR, with large, but decreasing scatter. The contribution of the cold neutral medium to the C II emission, as estimated from VLA H I data, is on average only 10%. Fits of modified black bodies to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the O I data before comparing it with models of photon dominated regions. Most of the ratios of C II/O I and (C II+O I)/TIR are consistent with two model solutions. The median ratios are consistent with one solution at n ∼ 2 × 102 cm−3, G0 ∼ 60, and a second low-FUV solution at n ∼ 104 cm−3, G0 ∼ 1.5. Conclusions. The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ∼1. A fraction of the gas may, however, be represented by the second solution.
We study the post-main-sequence stars in NGC 604, the most luminous H ii region in M33. A number of Wolf-Rayet (WR) stars and one red supergiant (RSG) were discovered earlier. Based on the broad-band ...photometry of the region, we present evidence that is consistent with the presence of this RSG and with three more RSG candidates. Using spectral energy distribution (SED) fitting based on Hubble Space Telescope UVIJHK photometry, we estimate the ages of the WR stars and RSGs and find that the two populations are from distinct formation episodes with ages of 3.2 ± 1.0 and 12.4 ± 2.1 Myr, respectively. The RSGs have greater extinctions towards their line of sight than the WR stars which is consistent with the production of a large amount of dust by the RSGs. Using the WR and RSG populations and similar SED fits to the most massive O stars, we estimate that the total stellar mass is (3.8 ± 0.6) × 105 M⊙. We find a large discrepancy between the expected Hα flux from such a massive cluster and the one observed. This suggests that 49+16
−19 per cent of the ionizing photons produced by massive stars in NGC 604 are leaking from this H ii region. We also suggest that the implications of an old RSG population mean that if NGC 604 were more distant and only observed in the infrared, it would be difficult to study the youngest burst of star formation due to the contamination of RSGs.
We study the post-main-sequence stars in NGC604, the most luminous Hii region in M33. A number of Wolf-Rayet (WR) stars and one red supergiant (RSG) were discovered earlier. Based on the broad-band ...photometry of the region, we present evidence that is consistent with the presence of this RSG and with three more RSG candidates. Using spectral energy distribution (SED) fitting based on Hubble Space Telescope UVIJHK photometry, we estimate the ages of the WR stars and RSGs and find that the two populations are from distinct formation episodes with ages of 3.2 ± 1.0 and 12.4 ± 2.1Myr, respectively. The RSGs have greater extinctions towards their line of sight than the WR stars which is consistent with the production of a large amount of dust by the RSGs. Using the WR and RSG populations and similar SED fits to the most massive O stars, we estimate that the total stellar mass is (3.8 ± 0.6) × 105M. We find a large discrepancy between the expected Hα flux from such a massive cluster and the one observed. This suggests that 49+16-19 per cent of the ionizing photons produced by massive stars in NGC604 are leaking from this Hii region. We also suggest that the implications of an old RSG population mean that if NGC604 were more distant and only observed in the infrared, it would be difficult to study the youngest burst of star formation due to the contamination of RSGs. PUBLICATION ABSTRACT
Galaxies in the Universe are distributed in a web-like structure characterized by different large-scale environments: dense clusters, elongated filaments, sheetlike walls and under-dense regions, ...called voids
. The low density in voids is expected to affect the properties of their galaxies. Indeed, previous studies
have shown that galaxies in voids are, on average, bluer and less massive, and have later morphologies and higher current star formation rates than galaxies in denser large-scale environments. However, it has never been observationally proved that the star formation histories (SFHs) in voids are substantially different from those in filaments, walls and clusters. Here we show that void galaxies have had, on average, slower SFHs than galaxies in denser large-scale environments. We also find two main SFH types present in all the environments: 'short-timescale' galaxies are not affected by their large-scale environment at early times but only later in their lives; 'long-timescale' galaxies have been continuously affected by their environment and stellar mass. Both types have evolved more slowly in voids than in filaments, walls and clusters.
Using velocity tagging we have detected hydrogen from NGC 5426 falling onto its interacting partner NGC 5427. Our observations, with the GHaFaS Fabry-Perot spectrometer, produced maps of the two ...galaxies in H Delta *a surface brightness and radial velocity. We found emission with the range of velocities associated with NGC 5426 along lines of sight apparently emanating from NGC 5427, superposed on the velocity map of the latter. After excluding instrumental effects we assign the anomalous emission to gas pulled from NGC 5426 during its passage close to NGC 5427. Its distribution, more intense between the arms and just outside the disk of NGC 5427, and weak, or absent, in the arms, suggests that the infalling gas is behind the disk, ionized by Lyman continuum photons escaping from NGC 5427. Modeling this, we estimate the distances of these gas clouds behind the plane: a few hundred parsecs to a few kiloparsecs. We also estimate the mass of the infalling (ionized plus neutral) gas, finding an infall rate of 10 M per year, consistent with the high measured star formation rate across the disk of NGC 5427 and with the detected circumnuclear galactic wind.
ABSTRACT
Atacama Large Millimeter/submillimeter Array (ALMA) observations revealed the presence of significant amounts of dust in the first Gyr of Cosmic time. However, the metal and dust build-up ...picture remains very uncertain due to the lack of constraints on metallicity. JWST has started to reveal the metal content of high-redshift targets, which may lead to firmer constraints on high-redshift dusty galaxies evolution. In this work, we use detailed chemical and dust evolution models to explore the evolution of galaxies within the ALMA Reionization Era Bright Emission Line Survey (REBELS) survey, testing different metallicity scenarios that could be inferred from JWST observations. In the models, we track the build-up of stellar mass using non-parametric star formation histories for REBELS galaxies. Different scenarios for metal and dust evolution are simulated by allowing different prescriptions for gas flows and dust processes. The model outputs are compared with measured dust scaling relations, by employing metallicity-dependent calibrations for the gas mass based on the C ii 158 μm line. Independently of the galaxies metal content, we found no need for extreme dust prescriptions to explain the dust masses revealed by ALMA. However, different levels of metal enrichment will lead to different dominant dust production mechanisms, with stardust production dominant over other interstellar medium dust processes only in the metal-poor case. This points out how metallicity measurements from JWST will significantly improve our understanding of the dust build-up in high-redshift galaxies. We also show that models struggle to reproduce observables such as dust-to-gas and dust-to-stellar ratios simultaneously, possibly indicating an overestimation of the gas mass through current calibrations, especially at high metallicities.
Context.
Void galaxies are essential for understanding the physical processes that drive galaxy evolution because they are less affected by external factors than galaxies in denser environments, that ...is, in filaments, walls, and clusters. The stellar metallicity of a galaxy traces the accumulated fossil record of the star formation through the entire life of the galaxy. A comparison of the stellar metallicity of galaxies in various environments, including voids, filaments, walls, and clusters can provide valuable insights into how the large-scale environment affects the chemical evolution of the galaxy.
Aims.
We present the first comparison of the relation of the total stellar mass versus central stellar metallicity between galaxies in voids, filaments, walls, and clusters with different star formation history (SFH) types, morphologies, and colours for stellar masses between 10
8.0
to 10
11.5
solar masses and redshift 0.01 <
z
< 0.05. We aim to better understand how the large-scale structure affects galaxy evolution by studying the stellar mass-metallicity relation of thousands of galaxies, which allows us to make a statistically sound comparison between galaxies in voids, filaments, walls, and clusters.
Methods.
We applied non-parametric full spectral fitting techniques (pPXF and STECKMAP) to 10 807 spectra from the SDSS-DR7 (987 in voids, 6463 in filaments and walls, and 3357 in clusters) and derived their central mass-weighted average stellar metallicity (M/H
M
).
Results.
We find that galaxies in voids have slightly lower stellar metallicities on average than galaxies in filaments and walls (by ∼0.1 dex), and they are much lower than those of galaxies in clusters (by ∼0.4 dex). These differences are more significant for low-mass (∼10
9.25
M
⊙
) than for high-mass galaxies, for long-timescale SFH (extended along time) galaxies than for short-timescale SFHs (concentrated at early times) galaxies, for spiral than for elliptical galaxies, and for blue than for red galaxies.
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