E. Mentuch | The University of Texas at Austin (original) (raw)
Papers by E. Mentuch
Proceedings of the International Astronomical Union, 2006
We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density... more We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically-selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place.
The Astrophysical Journal, 2009
We present the results of NICMOS imaging of a sample of 19 high mass passively evolving galaxies ... more We present the results of NICMOS imaging of a sample of 19 high mass passively evolving galaxies with 1.2 < z < 2, taken primarily from the Gemini Deep Deep Survey (GDDS). Around 80% of galaxies in our GDDS sample have spectra dominated by stars with ages 1 Gyr. Our rest-frame R-band images show that most of these objects have compact regular morphologies which follow the classical R 1/4 law. These galaxies scatter along a tight sequence in the size vs. surface brightness parameter space which defines the Kormendy relation. Around one-third (3/10) of the massive red objects in the GDDS sample are extraordinarily compact, with effective radii under one kiloparsec. Our NICMOS observations allow the detection of such systems more robustly than is possible with optical (rest-frame UV) data, and while similar systems have been seen at z 2, this is the first time such systems have been detected in a rest-frame optical survey at 1.2 < z < 2. We refer to these compact galaxies as 'red nuggets', and note that similarly compact massive galaxies are completely absent in the nearby Universe. We introduce a new 'stellar mass Kormendy relation' (stellar mass density vs size) which we use to single out the effects of size evolution from those of luminosity and color evolution in stellar populations. The 1 < z < 2 passive galaxies have mass densities that are an order of magnitude larger then early type galaxies today and are comparable to the compact distant red galaxies at 2 < z < 3. We briefly consider mechanisms for size evolution in contemporary models focusing on equalmass mergers and adiabatic expansion driven by stellar mass loss. Neither of these mechanisms appears able to transform the high-redshift Kormendy relation into its local counterpart, leaving the origin and fate of these compact 'red nuggets' unresolved.
The Astrophysical Journal, 2007
We describe a compact cluster of massive red galaxies at z = 1.51 discovered in one of the Gemini... more We describe a compact cluster of massive red galaxies at z = 1.51 discovered in one of the Gemini Deep Deep Survey (GDDS) fields. Deep imaging with Near Infrared Camera and Multi Object Spectrometer (NICMOS) on the Hubble Space Telescope reveals a high density of galaxies with red optical to near-IR colors surrounding a galaxy with a spectroscopic redshift of 1.51. Mid-IR imaging with Infrared Array Camera (IRAC) on the Spitzer Space telescope shows that these galaxies have spectral energy distributions that peak between 3.6µm and 4.5µm. Fits to 12-band photometry reveal 12 or more galaxies with spectral shapes consistent with z = 1.51. Most are within ∼ 170 co-moving kpc of the GDDS galaxy. Deep F814W images with the Advanced Camera for Surveys (ACS) on HST reveal that these galaxies are a mix of early-type galaxies, disk galaxies and close pairs. The total stellar mass enclosed within a sphere of 170 kpc in radius is > 8 × 10 11 M ⊙ . The colors of the most massive
The Astrophysical Journal, 2007
We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the cumulative m... more We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purposewritten morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z ∼ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range.
The Astrophysical Journal, 2009
A broad continuum excess in the near-infrared, peaking in the rest frame at 2-5 μm, is detected i... more A broad continuum excess in the near-infrared, peaking in the rest frame at 2-5 μm, is detected in a spectroscopic sample of 88 galaxies at 0.5 < z < 2.0 taken from the Gemini Deep Deep Survey. Line emission from polycyclic aromatic hydrocarbons (PAHs) at 3.3 μm alone cannot explain the excess, which can be fit by a spectral component consisting of a template of PAH emission lines superposed on a modified blackbody of temperature T ∼ 850 K. The luminosity of this near-infrared excess emission at 3 μm is found to be correlated with the star formation rate of the galaxy. The origin of the near-infrared excess is explored by examining similar excesses observed locally in massive star-forming regions, reflection and planetary nebulae, post-asymptotic giant branch stars, and in the galactic cirrus. We also consider the potential contribution from dust heated around low-luminosity active galactic nuclei. We conclude that the most likely explanation for the 2-5 μm excess is the contribution from circumstellar disks around massive young stellar objects seen in the integrated light of high-redshift galaxies. Assuming circumstellar disks extend down to lower masses, as they do in our own Galaxy, the excess emission presents us with an exciting opportunity to measure the formation rate of planetary systems at cosmic epochs before our own solar system formed.
The Astrophysical Journal, 2012
We present Herschel observations of 62 early-type galaxies (ETGs), including 39 galaxies morpholo... more We present Herschel observations of 62 early-type galaxies (ETGs), including 39 galaxies morphologically classified as S0+S0a and 23 galaxies classified as ellipticals using SPIRE at 250, 350 and 500 µm as part of the volume-limited Herschel Reference Survey (HRS). We detect dust emission in 24% of the ellipticals and 62% of the S0s. The mean temperature of the dust is T d = 23.9 ± 0.8 K, warmer than that found for late-type galaxies in the Virgo Cluster. The mean dust mass for the entire detected early-type sample is logM d = 6.1 ± 0.1 M ⊙ with mean dust-to-stellar mass ratio of log(M d /M * ) = −4.3 ± 0.1. Including the non-detections, these parameters are logM d = 5.6 ± 0.1 and log(M d /M * ) = −5.1 ± 0.1 respectively. The average dust-to-stellar mass ratio for the early-type sample is fifty times lower, with larger dispersion, than the spiral galaxies observed as part of the HRS, and there is an order of magnitude decline in M d /M * between the S0s and ellipticals. We use UV and optical photometry to show that virtually all the galaxies lie close to the red sequence yet the large number of detections of cool dust, the gas-to-dust ratios and the ratios of far-infrared to radio emission all suggest that many ETGs contain a cool interstellar medium similar to that in late-type galaxies. We show that the sizes of the dust sources in S0s are much smaller than those in early-type spirals and the decrease in the dust-to-stellar mass ratio from early-type spirals to S0s cannot simply be explained by an increase in the bulge-to-disk ratio. These results suggest that the disks in S0s contain much less dust (and presumably gas) than the disks of early-type spirals and this cannot be explained simply by current environmental effects, such as ram-pressure stripping. The wide range in the dust-to-stellar mass ratio for ETGs and the lack of a correlation between dust mass and optical luminosity suggest that much of the dust in the ETGs detected by Herschel has been acquired as the result of interactions, although we show these are unlikely to have had a major effect on the stellar masses of the ETGs. The Herschel observations tentatively suggest that in the most massive systems, the mass of interstellar medium is unconnected to the evolution of the stellar populations in these galaxies.
The Astrophysical Journal, 2010
We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies comm... more We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies common to the Spitzer Infrared Nearby Galaxies Survey and the Large Galaxy Atlas Survey. Each galaxy was separated into regions of increasingly red near-infrared colors. In the absence of dust extinction and other non-stellar emission, stellar populations are shown to have relatively constant NIR colors, independent of age. In regions of high star formation, the average intensity of pixels in red-excess regions (at 1.25 µm, 3.6 µm, 4.5 µm, 5.6 µm, 8.0 µm and 24 µm) scales linearly with the intrinsic intensity of Hα emission, and thus with the star-formation rate within the pixel. This suggests that most NIR-excess regions are not red because their light is being depleted by absorption. Instead, they are red because additional infrared light is being contributed by a process linked to star-formation. This is surprising because the shorter wavelength bands in our study (1.25 µm-5.6 µm) do not probe emission from cold (10-20 K) and warm (50-100 K) dust associated with star-formation in molecular clouds. However, emission from hot dust (700-1000 K) and/or Polycyclic Aromatic Hydrocarbon molecules can explain the additional emission seen at the shorter wavelengths in our study. The contribution from hot dust and/or PAH emission at 2 µm-5 µm and PAH emission at 5.6 µm and 8.0 µm scales linearly with warm dust emission at 24 µm and the intrinsic Hα emission. Since both are tied to the star-formation rate, our analysis shows that the NIR excess continuum emission and PAH emission at ∼ 1 − 8 µm can be added to spectral energy distribution models in a very straight-forward way, by simply adding an additional component to the models that scales linearly with star-formation rate. Recent work by and shows that a good estimator for the starformation rate emerges from the linear combination of a galaxy's near-UV or visible-wavelength emission (either UV continuum or line fluxes, attenuated by dust) and its
Monthly Notices of the Royal Astronomical Society, 2012
We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIR... more We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIRE instruments on board the Herschel Space Observatory, at 70, 160, 250, 350 and 500 µm, as well as new CO J = 3−2 observations taken with the HARP-B instrument on the JCMT. Using a single component modified blackbody, we model the dust spectral energy distribution within the disk of the galaxy using all five Herschel wavebands, and find dust temperatures of ∼ 30 K towards the centre of the disk and a smoothly decreasing trend to ∼ 20 K with increasing radius. We find a total dust mass of (1.59 ± 0.05) × 10 7 M ⊙ , and a total gas mass of (2.7 ± 0.2) × 10 9 M ⊙ . The average gas-to-dust mass ratio is 103 ± 8 but we find an interesting increase in this ratio to approximately 275 toward the centre of Cen A. We discuss several possible physical processes that may be causing this effect, including dust sputtering, jet entrainment and systematic variables such as the X CO factor. Dust sputtering by X-rays originating in the AGN or the removal of dust by the jets are our most favoured explanations.
Monthly Notices of the Royal Astronomical Society, 2012
... A. Boselli,8 DL Clements,3 A. Cooray,9 JI Davies,4 SA Eales,4 S. Madden,5 MJ Page10 and L. Sp... more ... A. Boselli,8 DL Clements,3 A. Cooray,9 JI Davies,4 SA Eales,4 S. Madden,5 MJ Page10 and L. Spinoglio11 1Department of Physics &amp;amp;amp;amp;amp; Astronomy, McMaster University ... (2) We use the extinction-corrected Hα fluxes given by this equation as a star formation tracer in our analysis. ...
Monthly Notices of the Royal Astronomical Society, 2012
We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground... more We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground-based optical and near-infrared data to understand how dust heating in the nearby face-on spiral galaxies M81, M83, and NGC 2403 is affected by the starlight from all stars and by the radiation from star forming regions. We find that 70/160 µm surface brightness ratios tend to be more strongly influenced by star forming regions. However, the 250/350 µm and 350/500 µm surface brightness ratios are more strongly affected by the light from the total stellar populations, suggesting that the dust emission at >250 µm originates predominantly from a component that is colder than the dust seen at <160 µm and that is relatively unaffected by star formation activity. We conclude by discussing the implications of this for modelling the spectral energy distributions of both nearby and more distant galaxies and for using farinfrared dust emission to trace star formation.
The Astrophysical Journal, 2011
Astronomy & Astrophysics, 2012
Context. Dust and stars play a complex game of interactions in the interstellar medium and around... more Context. Dust and stars play a complex game of interactions in the interstellar medium and around young stars. The imprints of those processes are visible in scaling relations between stellar characteristics, star formation parameters and dust properties. Aims. In the present work, we aim to examine dust scaling relations on a sub-kpc resolution in the Andromeda galaxy (M31). The goal is to investigate the properties of M31 both on a global and local scale and compare them to other galaxies of the local universe. Methods. New Herschel observations are combined with available data from GALEX, SDSS, WISE and Spitzer to construct a dataset covering UV to submm wavelengths. All images were brought to the beam size and pixel grid of the SPIRE 500 µm frame. This divides M31 in 22437 pixels of 36 arcseconds in size on the sky, corresponding to physical regions of 137 × 608 pc in the galaxy's disk. A panchromatic spectral energy distribution was modelled for each pixel and maps of the physical quantities were constructed. Several scaling relations were investigated, focussing on the interactions of dust with starlight. Results. We find, on a sub-kpc scale, strong correlations between M dust /M and NUV-r, and between M dust /M and µ (the stellar mass surface density). Striking similarities with corresponding relations based on integrated galaxies are found. We decompose M31 in four macro-regions based on their FIR morphology; the bulge, inner disk, star forming ring and the outer disk region. In the scaling relations, all regions closely follow the galaxy-scale average trends and behave like galaxies of different morphological type. The specific star formation characteristics we derive for these macro-regions give strong hints of an inside-out formation of the bulge-disk geometry, as well as an internal downsizing process. Within each macro-region, however, a great diversity in individual micro-regions is found, regardless of the properties of the macro-regions. Furthermore, we confirm that dust in the bulge of M31 is heated only by the old stellar populations. Conclusions. In general, the local dust scaling relations indicate that the dust content in M31 is maintained by a subtle interplay of past and present star formation. The similarity with galaxy-based relations strongly suggests that they are in situ correlations, with underlying processes that must be local in nature.
ABSTRACT We report the successful identification of the type of the supernova responsible for the... more ABSTRACT We report the successful identification of the type of the supernova responsible for the supernova remnant SNR 0509-675 in the Large Magellanic Cloud (LMC) using Gemini spectra of surrounding light echoes. The ability to classify outbursts associated with centuries-old remnants provides a new window into several aspects of supernova research and is likely to be successful in providing new constraints on additional LMC supernovae as well as their historical counterparts in the Milky Way Galaxy (MWG). The combined spectrum of echo light from SNR 0509-675 shows broad emission and absorption lines consistent with a supernova (SN) spectrum. We create a spectral library consisting of 26 SNe Ia and 6 SN Ib/c that are time-integrated, dust-scattered by LMC dust, and reddened by the LMC and MWG. We fit these SN templates to the observed light echo spectrum using χ 2 minimization as well as correlation techniques, and we find that overluminous 91T-like SNe Ia with ∆m15 < 0.9 match the observed spectrum best. Subject headings: ISM: individual(SNR 0509-67.5) — supernova:general — supernova remnants —
I present some new results related to our understanding of the masses of galaxies both in the loc... more I present some new results related to our understanding of the masses of galaxies both in the local and high-redshift Universe. At high-redshift new Spitzer data on galaxies in the Gemini Deep Deep Survey allow us a more accurate measure of stellar mass to light ratios (using rest frame near-IR light) showing a refinement of the measurements but not great discrepancies. In the local universe a new method is explored to estimate the baryonic mass function of galaxies including contributions from unseen HI. This points to an interesting result: that the baryonic mass function of galaxies may in fact be quite steep, of comparable slope to the mass function of dark matter haloes.
Proceedings of the International Astronomical Union, 2006
We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density... more We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically-selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place.
The Astrophysical Journal, 2009
We present the results of NICMOS imaging of a sample of 19 high mass passively evolving galaxies ... more We present the results of NICMOS imaging of a sample of 19 high mass passively evolving galaxies with 1.2 < z < 2, taken primarily from the Gemini Deep Deep Survey (GDDS). Around 80% of galaxies in our GDDS sample have spectra dominated by stars with ages 1 Gyr. Our rest-frame R-band images show that most of these objects have compact regular morphologies which follow the classical R 1/4 law. These galaxies scatter along a tight sequence in the size vs. surface brightness parameter space which defines the Kormendy relation. Around one-third (3/10) of the massive red objects in the GDDS sample are extraordinarily compact, with effective radii under one kiloparsec. Our NICMOS observations allow the detection of such systems more robustly than is possible with optical (rest-frame UV) data, and while similar systems have been seen at z 2, this is the first time such systems have been detected in a rest-frame optical survey at 1.2 < z < 2. We refer to these compact galaxies as 'red nuggets', and note that similarly compact massive galaxies are completely absent in the nearby Universe. We introduce a new 'stellar mass Kormendy relation' (stellar mass density vs size) which we use to single out the effects of size evolution from those of luminosity and color evolution in stellar populations. The 1 < z < 2 passive galaxies have mass densities that are an order of magnitude larger then early type galaxies today and are comparable to the compact distant red galaxies at 2 < z < 3. We briefly consider mechanisms for size evolution in contemporary models focusing on equalmass mergers and adiabatic expansion driven by stellar mass loss. Neither of these mechanisms appears able to transform the high-redshift Kormendy relation into its local counterpart, leaving the origin and fate of these compact 'red nuggets' unresolved.
The Astrophysical Journal, 2007
We describe a compact cluster of massive red galaxies at z = 1.51 discovered in one of the Gemini... more We describe a compact cluster of massive red galaxies at z = 1.51 discovered in one of the Gemini Deep Deep Survey (GDDS) fields. Deep imaging with Near Infrared Camera and Multi Object Spectrometer (NICMOS) on the Hubble Space Telescope reveals a high density of galaxies with red optical to near-IR colors surrounding a galaxy with a spectroscopic redshift of 1.51. Mid-IR imaging with Infrared Array Camera (IRAC) on the Spitzer Space telescope shows that these galaxies have spectral energy distributions that peak between 3.6µm and 4.5µm. Fits to 12-band photometry reveal 12 or more galaxies with spectral shapes consistent with z = 1.51. Most are within ∼ 170 co-moving kpc of the GDDS galaxy. Deep F814W images with the Advanced Camera for Surveys (ACS) on HST reveal that these galaxies are a mix of early-type galaxies, disk galaxies and close pairs. The total stellar mass enclosed within a sphere of 170 kpc in radius is > 8 × 10 11 M ⊙ . The colors of the most massive
The Astrophysical Journal, 2007
We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the cumulative m... more We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purposewritten morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z ∼ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range.
The Astrophysical Journal, 2009
A broad continuum excess in the near-infrared, peaking in the rest frame at 2-5 μm, is detected i... more A broad continuum excess in the near-infrared, peaking in the rest frame at 2-5 μm, is detected in a spectroscopic sample of 88 galaxies at 0.5 < z < 2.0 taken from the Gemini Deep Deep Survey. Line emission from polycyclic aromatic hydrocarbons (PAHs) at 3.3 μm alone cannot explain the excess, which can be fit by a spectral component consisting of a template of PAH emission lines superposed on a modified blackbody of temperature T ∼ 850 K. The luminosity of this near-infrared excess emission at 3 μm is found to be correlated with the star formation rate of the galaxy. The origin of the near-infrared excess is explored by examining similar excesses observed locally in massive star-forming regions, reflection and planetary nebulae, post-asymptotic giant branch stars, and in the galactic cirrus. We also consider the potential contribution from dust heated around low-luminosity active galactic nuclei. We conclude that the most likely explanation for the 2-5 μm excess is the contribution from circumstellar disks around massive young stellar objects seen in the integrated light of high-redshift galaxies. Assuming circumstellar disks extend down to lower masses, as they do in our own Galaxy, the excess emission presents us with an exciting opportunity to measure the formation rate of planetary systems at cosmic epochs before our own solar system formed.
The Astrophysical Journal, 2012
We present Herschel observations of 62 early-type galaxies (ETGs), including 39 galaxies morpholo... more We present Herschel observations of 62 early-type galaxies (ETGs), including 39 galaxies morphologically classified as S0+S0a and 23 galaxies classified as ellipticals using SPIRE at 250, 350 and 500 µm as part of the volume-limited Herschel Reference Survey (HRS). We detect dust emission in 24% of the ellipticals and 62% of the S0s. The mean temperature of the dust is T d = 23.9 ± 0.8 K, warmer than that found for late-type galaxies in the Virgo Cluster. The mean dust mass for the entire detected early-type sample is logM d = 6.1 ± 0.1 M ⊙ with mean dust-to-stellar mass ratio of log(M d /M * ) = −4.3 ± 0.1. Including the non-detections, these parameters are logM d = 5.6 ± 0.1 and log(M d /M * ) = −5.1 ± 0.1 respectively. The average dust-to-stellar mass ratio for the early-type sample is fifty times lower, with larger dispersion, than the spiral galaxies observed as part of the HRS, and there is an order of magnitude decline in M d /M * between the S0s and ellipticals. We use UV and optical photometry to show that virtually all the galaxies lie close to the red sequence yet the large number of detections of cool dust, the gas-to-dust ratios and the ratios of far-infrared to radio emission all suggest that many ETGs contain a cool interstellar medium similar to that in late-type galaxies. We show that the sizes of the dust sources in S0s are much smaller than those in early-type spirals and the decrease in the dust-to-stellar mass ratio from early-type spirals to S0s cannot simply be explained by an increase in the bulge-to-disk ratio. These results suggest that the disks in S0s contain much less dust (and presumably gas) than the disks of early-type spirals and this cannot be explained simply by current environmental effects, such as ram-pressure stripping. The wide range in the dust-to-stellar mass ratio for ETGs and the lack of a correlation between dust mass and optical luminosity suggest that much of the dust in the ETGs detected by Herschel has been acquired as the result of interactions, although we show these are unlikely to have had a major effect on the stellar masses of the ETGs. The Herschel observations tentatively suggest that in the most massive systems, the mass of interstellar medium is unconnected to the evolution of the stellar populations in these galaxies.
The Astrophysical Journal, 2010
We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies comm... more We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies common to the Spitzer Infrared Nearby Galaxies Survey and the Large Galaxy Atlas Survey. Each galaxy was separated into regions of increasingly red near-infrared colors. In the absence of dust extinction and other non-stellar emission, stellar populations are shown to have relatively constant NIR colors, independent of age. In regions of high star formation, the average intensity of pixels in red-excess regions (at 1.25 µm, 3.6 µm, 4.5 µm, 5.6 µm, 8.0 µm and 24 µm) scales linearly with the intrinsic intensity of Hα emission, and thus with the star-formation rate within the pixel. This suggests that most NIR-excess regions are not red because their light is being depleted by absorption. Instead, they are red because additional infrared light is being contributed by a process linked to star-formation. This is surprising because the shorter wavelength bands in our study (1.25 µm-5.6 µm) do not probe emission from cold (10-20 K) and warm (50-100 K) dust associated with star-formation in molecular clouds. However, emission from hot dust (700-1000 K) and/or Polycyclic Aromatic Hydrocarbon molecules can explain the additional emission seen at the shorter wavelengths in our study. The contribution from hot dust and/or PAH emission at 2 µm-5 µm and PAH emission at 5.6 µm and 8.0 µm scales linearly with warm dust emission at 24 µm and the intrinsic Hα emission. Since both are tied to the star-formation rate, our analysis shows that the NIR excess continuum emission and PAH emission at ∼ 1 − 8 µm can be added to spectral energy distribution models in a very straight-forward way, by simply adding an additional component to the models that scales linearly with star-formation rate. Recent work by and shows that a good estimator for the starformation rate emerges from the linear combination of a galaxy's near-UV or visible-wavelength emission (either UV continuum or line fluxes, attenuated by dust) and its
Monthly Notices of the Royal Astronomical Society, 2012
We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIR... more We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIRE instruments on board the Herschel Space Observatory, at 70, 160, 250, 350 and 500 µm, as well as new CO J = 3−2 observations taken with the HARP-B instrument on the JCMT. Using a single component modified blackbody, we model the dust spectral energy distribution within the disk of the galaxy using all five Herschel wavebands, and find dust temperatures of ∼ 30 K towards the centre of the disk and a smoothly decreasing trend to ∼ 20 K with increasing radius. We find a total dust mass of (1.59 ± 0.05) × 10 7 M ⊙ , and a total gas mass of (2.7 ± 0.2) × 10 9 M ⊙ . The average gas-to-dust mass ratio is 103 ± 8 but we find an interesting increase in this ratio to approximately 275 toward the centre of Cen A. We discuss several possible physical processes that may be causing this effect, including dust sputtering, jet entrainment and systematic variables such as the X CO factor. Dust sputtering by X-rays originating in the AGN or the removal of dust by the jets are our most favoured explanations.
Monthly Notices of the Royal Astronomical Society, 2012
... A. Boselli,8 DL Clements,3 A. Cooray,9 JI Davies,4 SA Eales,4 S. Madden,5 MJ Page10 and L. Sp... more ... A. Boselli,8 DL Clements,3 A. Cooray,9 JI Davies,4 SA Eales,4 S. Madden,5 MJ Page10 and L. Spinoglio11 1Department of Physics &amp;amp;amp;amp;amp; Astronomy, McMaster University ... (2) We use the extinction-corrected Hα fluxes given by this equation as a star formation tracer in our analysis. ...
Monthly Notices of the Royal Astronomical Society, 2012
We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground... more We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground-based optical and near-infrared data to understand how dust heating in the nearby face-on spiral galaxies M81, M83, and NGC 2403 is affected by the starlight from all stars and by the radiation from star forming regions. We find that 70/160 µm surface brightness ratios tend to be more strongly influenced by star forming regions. However, the 250/350 µm and 350/500 µm surface brightness ratios are more strongly affected by the light from the total stellar populations, suggesting that the dust emission at >250 µm originates predominantly from a component that is colder than the dust seen at <160 µm and that is relatively unaffected by star formation activity. We conclude by discussing the implications of this for modelling the spectral energy distributions of both nearby and more distant galaxies and for using farinfrared dust emission to trace star formation.
The Astrophysical Journal, 2011
Astronomy & Astrophysics, 2012
Context. Dust and stars play a complex game of interactions in the interstellar medium and around... more Context. Dust and stars play a complex game of interactions in the interstellar medium and around young stars. The imprints of those processes are visible in scaling relations between stellar characteristics, star formation parameters and dust properties. Aims. In the present work, we aim to examine dust scaling relations on a sub-kpc resolution in the Andromeda galaxy (M31). The goal is to investigate the properties of M31 both on a global and local scale and compare them to other galaxies of the local universe. Methods. New Herschel observations are combined with available data from GALEX, SDSS, WISE and Spitzer to construct a dataset covering UV to submm wavelengths. All images were brought to the beam size and pixel grid of the SPIRE 500 µm frame. This divides M31 in 22437 pixels of 36 arcseconds in size on the sky, corresponding to physical regions of 137 × 608 pc in the galaxy's disk. A panchromatic spectral energy distribution was modelled for each pixel and maps of the physical quantities were constructed. Several scaling relations were investigated, focussing on the interactions of dust with starlight. Results. We find, on a sub-kpc scale, strong correlations between M dust /M and NUV-r, and between M dust /M and µ (the stellar mass surface density). Striking similarities with corresponding relations based on integrated galaxies are found. We decompose M31 in four macro-regions based on their FIR morphology; the bulge, inner disk, star forming ring and the outer disk region. In the scaling relations, all regions closely follow the galaxy-scale average trends and behave like galaxies of different morphological type. The specific star formation characteristics we derive for these macro-regions give strong hints of an inside-out formation of the bulge-disk geometry, as well as an internal downsizing process. Within each macro-region, however, a great diversity in individual micro-regions is found, regardless of the properties of the macro-regions. Furthermore, we confirm that dust in the bulge of M31 is heated only by the old stellar populations. Conclusions. In general, the local dust scaling relations indicate that the dust content in M31 is maintained by a subtle interplay of past and present star formation. The similarity with galaxy-based relations strongly suggests that they are in situ correlations, with underlying processes that must be local in nature.
ABSTRACT We report the successful identification of the type of the supernova responsible for the... more ABSTRACT We report the successful identification of the type of the supernova responsible for the supernova remnant SNR 0509-675 in the Large Magellanic Cloud (LMC) using Gemini spectra of surrounding light echoes. The ability to classify outbursts associated with centuries-old remnants provides a new window into several aspects of supernova research and is likely to be successful in providing new constraints on additional LMC supernovae as well as their historical counterparts in the Milky Way Galaxy (MWG). The combined spectrum of echo light from SNR 0509-675 shows broad emission and absorption lines consistent with a supernova (SN) spectrum. We create a spectral library consisting of 26 SNe Ia and 6 SN Ib/c that are time-integrated, dust-scattered by LMC dust, and reddened by the LMC and MWG. We fit these SN templates to the observed light echo spectrum using χ 2 minimization as well as correlation techniques, and we find that overluminous 91T-like SNe Ia with ∆m15 < 0.9 match the observed spectrum best. Subject headings: ISM: individual(SNR 0509-67.5) — supernova:general — supernova remnants —
I present some new results related to our understanding of the masses of galaxies both in the loc... more I present some new results related to our understanding of the masses of galaxies both in the local and high-redshift Universe. At high-redshift new Spitzer data on galaxies in the Gemini Deep Deep Survey allow us a more accurate measure of stellar mass to light ratios (using rest frame near-IR light) showing a refinement of the measurements but not great discrepancies. In the local universe a new method is explored to estimate the baryonic mass function of galaxies including contributions from unseen HI. This points to an interesting result: that the baryonic mass function of galaxies may in fact be quite steep, of comparable slope to the mass function of dark matter haloes.