arXiv subjects

Jesse D. Bregman

Publications and source records attributed to Jesse D. Bregman.

9 recordsLinked to original sources

arXiv2026

PDRs4All: XVIII. The evolution of the PAH ionisation and PAH size distribution across the Orion Bar

We investigate the evolution of the PAH population's charge state and size across key physical zones in the Orion Bar, which include the HII region, the atomic PDR (APDR), and three HI/H2 dissociation fronts (DF1, DF2, and DF3). Utilising the NASA Ames PAH Infrared Spectroscopic Database (PAHdb) and the pyPAHdb spectral modelling tool, we analysed the MIRI-MRS observations of the Orion Bar from the "PDRs4All" ERS Program. pyPAHdb modelling reveals the fractional contribution of the different PAH charge states and sizes to the total PAH emission across the Orion Bar. Cationic PAH emission peaks in the APDR region, where neutral PAHs have minimal contribution. Emission from neutral PAHs peaks in the HII region that consists of emission from a face-on PDR associated to the background OMC-1 molecular cloud, and in the molecular cloud regions past DF2. PAH anions are observed deep within the DF2 and DF3 zones. The average PAH size ranges between ~$60-74$ Nc. The modelling reveals regions of top-down PAH formation at the ionisation front, and bottom-up PAH formation within the molecular cloud region. The PAH ionisation parameter $γ$ ranges between ~$2-9 x 10^4$. Intensity ratios tracing PAH ionisation scale well with $γ$ in regions encompassing edge-on or face-on PDR emission, but their correlation weakens within the molecular cloud zone. Modelling of the $5-15$ $μ$m PAH spectrum with pyPAHdb achieves comprehensive characterization of the net contribution of neutral and cationic PAHs across different environments, whereas empirical PAH proxy intensity ratio tracers can be highly variable and unreliable outside regions dominated by PDR emission. The derived average PAH size in the different physical zones is consistent with a view of PAHs being more extensively subjected to ultraviolet processing closer to the ionisation front, and less affected within the molecular cloud.

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arXiv2025

SPHEREx: Aromatics, Aliphatics and PAH Size across the Iris Nebula

Observations by the SpectroPhotometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) are combined with Spitzer spectral map data to study the aromatic, aliphatic, and PAH size evolution across the northwest photo-dissociation region (PDR) of the Iris Nebula (NGC7023). The 3.3-3.4 $μ$m complex (I$_{3.3}$) and 11.2 $μ$m (I$_{11.2}$) PAH band strength are determined through direct integration. In addition, the former is decomposed into a 3.3 (I'$_{3.3}$) and 3.4 $μ$m (I'$_{3.4}$) sub-feature by fitting SPHEREx bandpass-integrated photometry using a modeled, highly sampled, multi-component spectrum. I$_{3.3}$, I$_{11.2}$, I'$_{3.3}$, and I'$_{3.4}$ all peak at the PDR. The NASA Ames PAH IR Spectroscopic Database is used to obtain the average number of carbon atoms ($\overline{\rm N_{C}}$) and small PAH fraction ($f_{\rm small}$) by fitting the isolated PAH component of the Spitzer segment; $70\lesssim\overline{N_{C}}\lesssim76$ and $0.24\lesssim\text{f}_{\rm small}\lesssim0.36$. I'$_{3.4}$/I'$_{3.4}$, I$_{11.2}$/I$_{3.3}$, $\overline{\rm N_{C}}$, and $f_{\rm small}$ all show a demarcation that matches the large-scale morphology of the region. For I'$_{3.3}$ and I'$_{3.4}$ this is reflected by two distinct trends when plotted against each other, one associated with the dense, the other with the diffuse medium; $[N_{\rm H,ali}/N_{\rm H,aro}]_{\rm dense}$ = 0.42$\pm$0.01 and $[N_{\rm H,ali}/N_{\rm H,aro}]_{\rm diffuse}$ = 0.10$\pm$0.01. $\overline{\rm N_{C}}$ and $f_{\rm small}$ are tentatively correlated with I$_{11.2}$/I$_{3.3}$ (R=0.54$\pm$0.05 and -0.45$\pm$0.05, respectively). A wider variety of large(r) extended interstellar medium objects is required to tighten the correlations, turn them into quantitative calibrators for PAH size, and pin down the discrepancy of correlations with I'$_{3.3}$ involved.

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arXiv2024

A sensitivity analysis of the modeling of Polycyclic Aromatic Hydrocarbon emission in galaxies

We have conducted a sensitivity analysis on the mid-infrared spectral decomposition of galaxies and the modeling of the PAH emission spectrum with the NASA Ames PAH Infrared Spectroscopic Database (PAHdb) to assess the variance on the average galaxy PAH population properties under a grid of different modeling parameters. We find that the SL and SL+LL Spitzer-IRS decomposition with PAHFIT provides consistent modeling and recovery of the 5-15 $μ$m PAH emission spectrum. For PAHdb modeling, application of a redshift to the calculated spectra to account for anharmonic effects introduces a $15\%$-$20\%$ variance on the derived parameters, while its absence improves the fits by $\sim13\%$. The 4.00-$α$ release of PAHdb achieves the complete modeling of the 6-15 $μ$m PAH spectrum, including the full 6.2 $μ$m band, improving the average fitting uncertainty by a factor of 2. The optimal PAHdb modeling configuration requires selection of pure PAHs without applying a redshift to the bands. Although quantitatively the PAHdb-derived parameters change under different modeling configurations or database versions, their variation follows a linear scaling, with previously reported trends remaining qualitatively valid. PAHdb modeling of JWST observations, and JWST observations smoothed and resampled to the Spitzer-IRS resolution and dispersion have consistent PAHdb derived parameters. Decomposition with different codes, such as PAHFIT and CAFE, produce PAH emission spectra with noticeable variation in the 11-15~$μ$m region, driving a $\sim7\%$ difference in the neutral PAH fraction under PAHdb modeling. A new library of galaxy PAH emission templates is delivered to be utilized in galaxy SED modeling.

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arXiv2024

The Background Interstellar Medium as Observed from Off-Order Low-Resolution Spitzer-IRS Spectra

Spitzer 'hidden' observations of the background are used to construct a catalog of 4,090 spectra and examine the signature of polycyclic aromatic hydrocarbon (PAH) molecules and their connection to extinction by dust. A strong positive correlation is recovered between WISE12, E(B-V), and the 11.2 $μ$m PAH band. For 0.06 $\leq$ E(B-V) $\leq$ 5.0, correlations of the 6.2, 11.2, and 12.7 $μ$m PAH band are positive with E(B-V). Three dust temperature regimes are revealed. Correlations with WISE12 are well-constrained and that with 12.7/11.2 is flat. Decomposition with the NASA Ames PAH IR Spectroscopic Database reveals a tentative positive correlation between the 6.2/11.2 and the PAH ionization fraction, while that with 12.7/11.2 is slightly negative, suggesting PAH structural changes. The relation with PAH size and 6.2/11.2 is negative, while that with 12.7/11.2 is positive. Averaging spectra into five E(B-V) and three T$_{\rm dust}$ bins shows an evolution in PAH emission and variations in 12.7/11.2. Database-fits show an increase in $f_{\rm i}$ and the PAH ionization parameter $γ$, but a more stable large PAH fraction. While the largest $γ$s are associated with the highest T$_{\rm dust}$, there is no one-to-one correlation. The analysis is hampered by low-quality data at short wavelengths. There are indications that PAHs in the more-diffuse backgrounds behave differently from those in the general interstellar medium. However, they are often still associated with larger scale filamentary cloud-like structures. The spectra and auxiliary data have been made available through the Ames Background Interstellar Medium Spectral Catalog and may guide JWST programs.

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arXiv2006

The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions

The mean ages of early-type galaxies obtained from the analysis of optical spectra, give a mean age of 8 Gyr at z = 0, with 40% being younger than 6 Gyr. Independent age determinations are possible by using infrared spectra (5-21 microns), which we have obtained with the Infrared Spectrograph on the Spitzer Observatory. This age indicator is based on the collective mass loss rate of stars, where mass loss from AGB stars produces a silicate emission feature at 9-12 microns. This feature decreases more rapidly than the shorter wavelength continuum as a stellar population ages, providing an age indicator. From observations of 30 nearby early-type galaxies, 29 show a spectral energy distribution dominated by stars and one has significant emission from the ISM and is excluded. The infrared age indicators for the 29 galaxies show them all to be old, with a mean age of about 10 Gyr and a standard deviation of only a few Gyr. This is consistent with the ages inferred from the values of M/L_B, but is inconsistent with the ages derived from the optical line indices, which can be much younger. All of these age indicators are luminosity-weighted and should be correlated, even if multiple-age components are considered. The inconsistency indicates that there is a significant problem with either the infrared and the M/L_B ages, which agree, or with the ages inferred from the optical absorption lines.

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arXiv2004

Variations of the Mid-IR Emission Spectrum in Reflection Nebulae

Using spatial-spectral data cubes of reflection nebulae obtained by ISOCAM, we have observed a shift in the central wavelength of the 7.7 um band within several reflection nebulae. This band, composed of components at 7.85 um and 7.65 um, shows a centroid shift from 7.75 um near the edge of the nebulae to 7.65 um towards the center of the nebulae as the shorter wavelength component becomes relatively stronger. The behavior of the 7.7 um band center can be explained either by assuming that anions are the origin of the 7.85 um band and cations the 7.65 um band, or that the band center wavelength depends on the chemical nature of the PAHs. The ratio of the 11.3/7.7 um bands also changes with distance from the central star, first rising from the center towards the edge of the nebula, then falling at the largest distances from the star, consistent with the 11.3/7.7 um band ratio being controlled by the PAH ionization state.

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arXiv2003

Cold Dust in Early-Type Galaxies. I. Observations

We describe far infrared observations of early-type galaxies selected from the ISO archive. This rather inhomogeneous sample includes 39 giant elliptical galaxies and 14 S0 (or later) galaxies. These galaxies were observed using a variety of different observing modes, each of which requires different and often rather elaborate photometric reduction procedures. The ISO background data agrees well with COBE-DIRBE results to which we have renormalized our calibrations. As a further check, the ISO fluxes from galaxies at 60 and 100 microns agree very well with those previously observed with IRAS at these wavelengths. The spatial resolution of ISO is several times greater than that of IRAS and the ISO observations extend out to 200 microns which views a significantly greater mass of colder dust not assessable to IRAS. Most of the galaxies are essentially point sources at ISO resolution, but a few are clearly extended at FIR wavelengths with image sizes that increase with FIR wavelength. The integrated far infrared luminosities do not correlate with optical luminosities, suggesting that the dust may have an external, merger-related origin. In general the far infrared spectral energy distributions can be modeled with dust at two temperatures, ~ 43 K and ~ 20 K, which probably represent limits of a continuous range of temperatures. The colder dust component dominates the total mass of dust, which is typically more than ten times larger than the dust masses previously estimated for the same galaxies using IRAS observations. For S0 galaxies we find that the optically normalized far-infrared luminosity $L_{FIR} / L_B$ correlates strongly with the mid-infrared luminosity $L_{15μ\rm{m}} / L_B$, but that correlation is weaker for elliptical galaxies.

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arXiv2003

Dust in Hot Gas: Far Infrared Emission from Three Local Elliptical Galaxies

We present far-IR ISO observations of three early-type galaxies in the Virgo cluster. The data were recorded using the ISOPHOT instrument in both the P32 oversampled maps and the P39/37 sparse maps. The maps reach the limiting sensitivity of the ISOPHOT instrument at 60, 90, and 180$μ$m. Two of the most prominent elliptical galaxies in Virgo -- NGC 4472 and NGC 4649 -- clearly show no emission at far-IR wavelengths at a level of few tens of mJy, but NGC 4636 is detected at all three wavelengths. We have computed the far-IR emission from dust for NGC4472 and NGC4636 under the assumption that dusty outflows from evolving red giant stars are continuously supplying dust to the interstellar medium and that the grains, once diffused into the interstellar medium, are sputtered away by collisions with ions. While the calculated fluxes are consistent with the observed upper limits for NGC4472, the dust emission detected in NGC4636 support the hypothesis that additional dust has been accreted in a very recent ($\lta$ few $10^8$ yrs) merger with a dusty, gas-rich galaxy.

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arXiv2002

Mid-IR Observations of Mass Loss in Elliptical Galaxies

Early-type galaxies exhibit thermal and molecular resonance emission from dust that is shed and heated through stellar mass loss as a subset of the population moves through the AGB phase of evolution. Because this emission can give direct insight into stellar evolution in addition to galactic stellar mass loss and ISM injection rates, we conducted a program to search for this signature emission with CAM on ISO. We obtained 6-15 micron imaging observations in six narrow bands for nine elliptical galaxies; every galaxy is detected in every band. For wavelengths shorter than 9 microns, the spectra are well matched by a blackbody, originating from the K and M stars that dominate the integrated light of elliptical galaxies. However, at wavelengths between 9 and 15 microns, the galaxies display excess emission relative to the stellar photospheric radiation. Additional data taken with the fine resolution circular variable filter on one source clearly shows broad emission from 9 to 15 microns, peaking around 10 microns. This result is consistent with the known, broad silicate feature at 9.7 microns, originating in the circumstellar envelopes of AGB stars. This emission is compared with studies of Galactic and LMC AGB stars to derive cumulative mass loss rates. In general, these mass loss rates agree with the expected ~0.8 solar masses per year value predicted by stellar evolutionary models. Both the photospheric and circumstellar envelope emission follow a de Vaucouleurs' R^{1/4} law, supporting the conclusion that the mid-infrared excess emission originates in the stellar component of the galaxies and acts as a tracer of AGB mass loss and mass injection into the ISM.

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