Publications (64)214.28 Total impact
-
Article: High Resolution IR Observations of the Starburst Ring in NGC 7552 -- One Ring to Rule Them All?
[show abstract] [hide abstract]
ABSTRACT: We observed the ring galaxy NGC 7552 with the mid-infrared (MIR) instrument VISIR at an angular resolution of 0.3"- 0.4" and with the near-infrared (NIR) integral-field spectrograph SINFONI on the VLT, and complement these observations with data from ISO and Spitzer. The starburst ring is clearly detected at MIR wavelengths at the location of the dust-extincted, dark ring seen in HST observations. This "ring", however, is a rather complex annular region of more than 100 parsec width. We find a large fraction of diffuse [Ne II] and PAH emission in the central region that is not associated with the MIR peaks on spatial scales of \sim30 pc. We do not detect MIR emission from the nucleus of NGC 7552, which is very prominent at optical and NIR continuum wavelengths. However, we have identified nine unresolved MIR peaks within the ring. The average extinction of these peaks is A(V)=7.4 and their total infrared luminosity is L(IR) = 2.1*10^10 Lo. The properties of these peaks are typical for MIR-selected massive clusters found in other galaxies. The ages of the MIR-selected clusters are in the range of 5.9\pm0.3 Myr. The age spread among the clusters of 0.8 Myr is small compared to the travel time of \sim5.6 Myr for half an orbit within the starburst ring. We find no strong evidence for a scenario where the continuous inflow of gas leads to the ongoing formation of massive clusters at the contact points between galactic bar and starburst ring. Instead, it appears more likely that the gas density build up more gradually over larger ring segments, and that the local physical conditions govern cluster formation. We note that the fundamental limitation on the accurate derivation of cluster age, mass and IMF slope is the lack of higher angular resolution.05/2012; -
Article: A Study of Heating and Cooling of the ISM in NGC 1097 with Herschel-PACS and Spitzer-IRS
[show abstract] [hide abstract]
ABSTRACT: NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar and an active nucleus. We present a detailed study of the spatial variation of the far infrared (FIR) [CII]158um and [OI]63um lines and mid-infrared H2 emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS, and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency ([CII]158um+[OI]63um)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7um PAH ratio is also lower in the ring, which may suggest a larger fraction of ionized PAHs, but no clear correlation with [CII]158{\mu}m/PAH(5.5 - 14um) is found. PAHs in the ring are responsible for a factor of two more [CII]158um and [OI]63um emission per unit mass than PAHs in the Enuc S. SED modeling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high intensity photodissociation regions (PDRs), in which case G0 ~ 10^2.3 and nH ~ 10^3.5 cm^-3 in the ring. For these values of G0 and nH PDR models cannot reproduce the observed H2 emission. Much of the the H2 emission in the starburst ring could come from warm regions in the diffuse ISM that are heated by turbulent dissipation or shocks.04/2012; -
Article: Resolving the Far-IR Line Deficit: Photoelectric Heating and Far-IR Line Cooling in NGC 1097 and NGC 4559
[show abstract] [hide abstract]
ABSTRACT: The physical state of interstellar gas and dust is dependent on the processes which heat and cool this medium. To probe heating and cooling of the interstellar medium over a large range of infrared surface brightness, on sub-kiloparsec scales, we employ line maps of [C II] 158 μm, [O I] 63 μm, and [N II] 122 μm in NGC 1097 and NGC 4559, obtained with the Photodetector Array Camera & Spectrometer on board Herschel. We matched new observations to existing Spitzer Infrared Spectrograph data that trace the total emission of polycyclic aromatic hydrocarbons (PAHs). We confirm at small scales in these galaxies that the canonical measure of photoelectric heating efficiency, ([C II] + [O I])/TIR, decreases as the far-infrared (far-IR) color, νf ν(70 μm) νf ν(100 μm), increases. In contrast, the ratio of far-IR cooling to total PAH emission, ([C II] + [O I])/PAH, is a near constant ~6% over a wide range of far-IR color, 0.5 < νf ν(70 μm) νf ν(100 μm) 0.95. In the warmest regions, where νf ν(70 μm) νf ν(100 μm) 0.95, the ratio ([C II] + [O I])/PAH drops rapidly to 4%. We derived representative values of the local ultraviolet radiation density, G 0, and the gas density, n H, by comparing our observations to models of photodissociation regions. The ratio G 0/n H, derived from fine-structure lines, is found to correlate with the mean dust-weighted starlight intensity, U, derived from models of the IR spectral energy distribution. Emission from regions that exhibit a line deficit is characterized by an intense radiation field, indicating that small grains are susceptible to ionization effects. We note that there is a shift in the 7.7/11.3 μm PAH ratio in regions that exhibit a deficit in ([C II] + [O I])/PAH, suggesting that small grains are ionized in these environments.The Astrophysical Journal 02/2012; 747(1):81. · 6.02 Impact Factor -
Article: Herschel Far-infrared and Submillimeter Photometry for the KINGFISH Sample of nearby Galaxies
[show abstract] [hide abstract]
ABSTRACT: New far-infrared and submillimeter photometry from the Herschel Space Observatory is presented for 61 nearby galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH) sample. The spatially integrated fluxes are largely consistent with expectations based on Spitzer far-infrared photometry and extrapolations to longer wavelengths using popular dust emission models. Dwarf irregular galaxies are notable exceptions, as already noted by other authors, as their 500 μm emission shows evidence for a submillimeter excess. In addition, the fraction of dust heating attributed to intense radiation fields associated with photodissociation regions is found to be (21 ± 4)% larger when Herschel data are included in the analysis. Dust masses obtained from the dust emission models of Draine & Li are found to be on average nearly a factor of two higher than those based on single-temperature modified blackbodies, as single blackbody curves do not capture the full range of dust temperatures inherent to any galaxy. The discrepancy is largest for galaxies exhibiting the coolest far-infrared colors.The Astrophysical Journal 01/2012; 745(1):95. · 6.02 Impact Factor -
Article: Calibrating Extinction-Free Star Formation Rate Diagnostics with 33GHz Free-Free Emission in NGC6946
[show abstract] [hide abstract]
ABSTRACT: Abridged: Using free-free emission measured in the Ka-band (26-40GHz) for 10 star-forming regions in the nearby galaxy NGC6946, including its starbursting nucleus, we compare a number of SFR diagnostics that are typically considered to be unaffected by interstellar extinction: i.e., non-thermal radio (i.e., 1.4GHz), total infrared (IR; 8-1000um), and warm dust (i.e., 24um) emission, along with the hybrid (obscured + unobscured) indicators of H\alpha+24um and UV+IR. The 33GHz free-free emission is assumed to provide the most accurate measure of the current SFR. Among the extranuclear star-forming regions, the 24um, H\alpha+24um and UV+IR SFR calibrations are in good agreement with the 33GHz free-free SFRs. However, each of the SFR calibrations relying on some form of dust emission overestimate the nuclear SFR by a factor of ~2. This is more likely the result of excess dust heating through an accumulation of non-ionizing stars associated with an extended episode of star formation in the nucleus rather than increased competition for ionizing photons by dust. SFR calibrations using the non-thermal radio continuum yield values which only agree with the free-free SFRs for the nucleus, and underestimate the SFRs from the extranuclear star-forming regions by a factor of ~2. This result likely arises from the CR electrons decaying within the starburst region with negligible escape compared to the young extranuclear star-forming regions. Finally, we find that the SFRs estimated using the total 33GHz emission agree well with the free-free SFRs due to the large thermal fractions present at these frequencies even when local diffuse backgrounds are not removed. Thus, rest-frame 33GHz observations may act as a reliable method to measure the SFRs of galaxies at increasingly high redshift without the need of ancillary radio data to account for the non-thermal emission.05/2011; -
Article: Multiwavelength Study of Chandra X-Ray Sources in the Antennae
[show abstract] [hide abstract]
ABSTRACT: We use WIRC, IR images of the Antennae (NGC 4038/4039) together with the extensive catalogue of 120 X-ray point sources (Zezas et al. 2006) to search for counterpart candidates. Using our proven frame-tie technique, we find 38 X-ray sources with IR counterparts, almost doubling the number of IR counterparts to X-ray sources first identified in Clark et al. (2007). In our photometric analysis, we consider the 35 IR counterparts that are confirmed star clusters. We show that the clusters with X-ray sources tend to be brighter, K_s ~16 mag, with (J-K_s) = 1.1 mag. We then use archival HST images of the Antennae to search for optical counterparts to the X-ray point sources. We employ our previous IR-to-X-ray frame-tie as an intermediary to establish a precise optical-to-X-ray frame-tie with <0.6 arcsec rms positional uncertainty. Due to the high optical source density near the X-ray sources, we determine that we cannot reliably identify counterparts. Comparing the HST positions to the 35 identified IR star cluster counterparts, we find optical matches for 27 of these sources. Using Bruzual-Charlot spectral evolutionary models, we find that most clusters associated with an X-ray source are massive, ~10^6 M_sun, young, ~10^6 yr, with moderate metallicities, Z=0.05. Comment: 9 page, 8 figures, accepted for publication in MNRAS08/2010; -
Article: Enhanced dust heating in the bulges of early-type spiral galaxies
[show abstract] [hide abstract]
ABSTRACT: Stellar density and bar strength should affect the temperatures of the cool (T ~ 20-30 K) dust component in the inner regions of galaxies, which implies that the ratio of temperatures in the circumnuclear regions to the disk should depend on Hubble type. We investigate the differences between cool dust temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting models to measurements between 70 and 500 microns. We attempt to quantify temperature trends in nearby disk galaxies, with archival data from Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired during the first phases of the Herschel observations for the KINGFISH (key insights in nearby galaxies: a far-infrared survey with Herschel) sample. We fit single-temperature modified blackbodies to far-infrared and submillimeter measurements of the central and disk regions of galaxies to determine the temperature of the component(s) emitting at those wavelengths. We present the ratio of central-region-to-disk-temperatures of the cool dust component of 13 nearby galaxies as a function of morphological type. We find a significant temperature gradient in the cool dust component in all galaxies, with a mean center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological types earlier than Sc, and only 9(+/-3)% hotter for later types. The temperature ratio is also correlated with bar strength, with only strongly barred galaxies having a ratio over 1.2. The strong radiation field in the high stellar density of a galactic bulge tends to heat the cool dust component to higher temperatures, at least in early-type spirals with relatively large bulges, especially when paired with a strong bar. Comment: Accepted for publication on the A&A Herschel Special Issue05/2010; -
Article: A Spitzer High-resolution Mid-Infrared Spectral Atlas of Starburst Galaxies
[show abstract] [hide abstract]
ABSTRACT: We present an atlas of Spitzer/IRS high-resolution (R ~ 600) 10-37 μm spectra for 24 well known starburst galaxies. The spectra are dominated by fine-structure lines, molecular hydrogen lines, and emission bands of polycyclic aromatic hydrocarbons (PAHs). Six out of the eight objects with a known active galactic nucleus (AGN) component show emission of the high excitation [Ne V] line. This line is also seen in one other object (NGC 4194) with, a priori, no known AGN component. In addition to strong PAH emission features in this wavelength range (11.3, 12.7, 16.4 μm), the spectra reveal other weak hydrocarbon features at 10.6, 13.5, 14.2 μm, and a previously unreported emission feature at 10.75 μm. An unidentified absorption feature at 13.7 μm is detected in many of the starbursts. We use the fine-structure lines to derive the abundance of neon and sulfur for 14 objects where the H I 7-6 line is detected. We further use the molecular hydrogen lines to sample the properties of the warm molecular gas. Several basic diagrams characterizing the properties of the sample are also shown. We have combined the spectra of all the pure starburst objects to create a high signal-to-noise ratio template, which is available to the community.The Astrophysical Journal Supplement Series 09/2009; 184(2):230. · 13.46 Impact Factor -
Article: Spitzer-IRS Study of the Antennae Galaxies NGC 4038/39
[show abstract] [hide abstract]
ABSTRACT: Using the Infrared Spectrograph on the Spitzer Space Telescope, we observed the Antennae galaxies obtaining spectral maps of the entire central region and high signal-to-noise 5-38 μm spectra of the two galactic nuclei and six infrared-luminous regions. The total infrared luminosity of our six IR peaks plus the two nuclei is L IR = 3.8 × 1010 L ☉, with their derived star formation rates ranging between 0.2 and 2 M ☉ yr–1, with a total of 6.6 M ☉ yr–1. None of the typical mid-IR tracers of active galactic nucleus activity is detected in either nucleus of the system, excluding the presence of a dust-enshrouded accretion disk. The hardest and most luminous radiation originates from two compact clusters in the southern part of the overlap region, which also have the highest dust temperatures. Polycyclic aromatic hydrocarbon (PAH) emission and other tracers of softer radiation are spatially extended throughout and beyond the overlap region, but regions with a harder and more intense radiation field show a reduced PAH strength. The strong H2 emission is rather confined around the nucleus of NGC 4039, where shocks appear to be the dominant excitation mechanism, and the southern part of the overlap region, where it traces the most recent starburst activity. The luminosity ratio between the warm molecular gas (traced by the H2 lines) and the total far-IR emission is ~ 1.6 × 10–4, similar to that found in many starbursts and ultraluminous infrared galaxies. The total mass of warm H2 in the Antennae is 2.5 × 107 M ☉, with a fraction of warm to total H2 gas mass of about 0.35%. The average warm H2 temperature is 302 ± 26 K and appears anticorrelated with the radiation field hardness, possibly due to an evolution of the photodissociation region (PDR) morphology. The previously reported tight correlation between the H2 and PAH emission was not found but higher total PAH emission to continuum ratios were found in PDRs with warmer gas.The Astrophysical Journal 06/2009; 699(2):1982. · 6.02 Impact Factor -
Article: The Mid-Infrared Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy
[show abstract] [hide abstract]
ABSTRACT: We present 5-38 μm mid-infrared spectra at a spectral resolution of R ≈ 65-130 of a large sample of 22 starburst nuclei taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The spectra show a vast range of starburst SEDs. The silicate absorption ranges from essentially no absorption to heavily obscured systems with an optical depth of τ9.8 μm ~ 5. The spectral slopes can be used to discriminate between starburst and AGN powered sources. The monochromatic continuum fluxes at 15 and 30 μm enable a remarkably accurate estimate of the total infrared luminosity of the starburst. We find that the PAH equivalent width is independent of the total starburst luminosity LIR as both continuum and PAH feature scale proportionally. However, the luminosity of the 6.2 μm feature scales with LIR and can be used to approximate the total infrared luminosity of the starburst. Although our starburst sample covers about a factor of 10 difference in the [Ne III]/[Ne II] ratio, we found no systematic correlation between the radiation field hardness and the PAH equivalent width or the 7.7 μm/11.3 μm PAH ratio. These results are based on spatially integrated diagnostics over an entire starburst region, and local variations may be "averaged out." It is presumably due to this effect that unresolved starburst nuclei with significantly different global properties appear spectrally as rather similar members of one class of objects.The Astrophysical Journal 12/2008; 653(2):1129. · 6.02 Impact Factor -
Article: Spectroscopic Redshifts to z > 2 for Optically Obscured Sources Discovered with the Spitzer Space Telescope
[show abstract] [hide abstract]
ABSTRACT: We have surveyed a field covering 9.0 deg2 within the NOAO Deep Wide-Field Survey region in Bootes with the Multiband Imaging Photometer on the Spitzer Space Telescope (SST) to a limiting 24 μm flux density of 0.3 mJy. Thirty-one sources from this survey with F24 μm > 0.75 mJy that are optically very faint (R 24.5 mag) have been observed with the low-resolution modules of the Infrared Spectrograph on SST (IRS). Redshifts derived primarily from strong silicate absorption features are reported here for 17 of these sources; 10 of these are optically invisible (R 26 mag), with no counterpart in BW, R, or I. The observed redshifts for 16 sources are 1.7 < z < 2.8. These represent a newly discovered population of highly obscured sources at high redshift with extreme infrared-to-optical ratios. Using IRS spectra of local galaxies as templates, we find that a majority of the sources have mid-infrared spectral shapes most similar to ultraluminous infrared galaxies powered primarily by active galactic nuclei. Assuming that the same templates also apply at longer wavelengths, bolometric luminosities exceed 1013 L☉.The Astrophysical Journal 12/2008; 622(2):L105. · 6.02 Impact Factor -
Article: Infrared Counterparts to Chandra X-Ray Sources in the Antennae
[show abstract] [hide abstract]
ABSTRACT: We use deep J (1.25 μm) and Ks (2.15 μm) images of the Antennae (NGC 4038/4039) obtained with the Wide-field InfraRed Camera on the Palomar 200 inch (5 m) telescope, together with the Chandra X-ray source list of Zezas and coworkers to search for infrared counterparts to X-ray point sources. We establish an X-ray/IR astrometric frame tie with ~0.5'' rms residuals over a ~4.3' field. We find 13 "strong" IR counterparts brighter than Ks = 17.8 mag and <1.0'' from X-ray sources, and an additional 6 "possible" IR counterparts between 1.0'' and 1.5'' from X-ray sources. Based on a detailed study of the surface density of IR sources near the X-ray sources, we expect only ~2 of the "strong" counterparts and ~3 of the "possible" counterparts to be chance superpositions of unrelated objects. Comparing both strong and possible IR counterparts to our photometric study of ~220 IR clusters in the Antennae, we find with a >99.9% confidence level that IR counterparts to X-ray sources are ΔMKs ~ 1.2 mag more luminous than average non-X-ray clusters. We also note that the X-ray/IR matches are concentrated in the spiral arms and "overlap" regions of the Antennae. This implies that these X-ray sources lie in the most "super" of the Antennae's super star clusters, and thus trace the recent massive star formation history here. Based on the NH inferred from the X-ray sources without IR counterparts, we determine that the absence of most of the "missing" IR counterparts is not due to extinction, but that these sources are intrinsically less luminous in the IR, implying that they trace a different (possibly older) stellar population. We find no clear correlation between X-ray luminosity classes and IR properties of the sources, although small-number statistics hamper this analysis.The Astrophysical Journal 12/2008; 658(1):319. · 6.02 Impact Factor -
Article: The Extraordinary Mid-infrared Spectrum of the Blue Compact Dwarf Galaxy SBS 0335–052
[show abstract] [hide abstract]
ABSTRACT: SBS 0335-052 is a blue compact dwarf galaxy (BCD) with one of the lowest known metallicities, Z ~ Z/41, making it a local example of how primordial starburst galaxies and their precursors might appear. A spectrum obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope clearly shows silicate absorption features and emission lines of [S IV] and [Ne III], and puts strong upper limits on the polycyclic aromatic hydrocarbon (PAH) emission features. The observed low-resolution spectrum (R ~ 90) extends from 5.3 to 35 μm and peaks at ~28 μm. The spectrum is compared to IRS observations of the prototypical starburst nucleus NGC 7714. SBS 0335-052 is quite unlike normal starburst galaxies, which show strong PAH bands, low-ionization emission lines, and a continuum peak near 80 μm. The continuum difference for λ > 30 μm implies a substantial reduction in the mass of cold dust. If the spectrum of this very low-metallicity galaxy is representative of star-forming galaxies at higher redshifts, it may be difficult to distinguish them from active galactic nuclei, which also show relatively featureless flat spectra in the mid-IR.The Astrophysical Journal Supplement Series 12/2008; 154(1):211. · 13.46 Impact Factor -
Article: Spitzer Infrared Spectrograph Spectroscopy of the Prototypical Starburst Galaxy NGC 7714
[show abstract] [hide abstract]
ABSTRACT: We present observations of the starburst galaxy NGC 7714 with the Infrared Spectrograph on board the Spitzer Space Telescope. The spectra yield a wealth of ionic and molecular features that allow a detailed characterization of its properties. NGC 7714 has an H II region-like spectrum with strong polycyclic aromatic hydrocarbon emission features. We find no evidence for an obscured active galactic nucleus, and with [Ne ]/[Ne ] ≈ 0.73, NGC 7714 lies near the upper end of normal-metallicity starburst galaxies. With very little silicate absorption and a temperature of the hottest dust component of 340 K, NGC 7714 is the perfect template for a young, unobscured starburst.The Astrophysical Journal Supplement Series 12/2008; 154(1):188. · 13.46 Impact Factor -
Article: PAH Emission from Ultraluminous Infrared Galaxies
[show abstract] [hide abstract]
ABSTRACT: We explore the relationships between the polycyclic aromatic hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far-infrared spectral slopes, optical spectroscopic classifications, and silicate optical depths in a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 μm PAH equivalent widths (EWs) in the sample span more than 2 orders of magnitude (~0.006-0.8 μm), and ULIRGs with H II-like optical spectra or steep far-infrared spectral slopes (S25/S60 < 0.2) typically have 6.2 μm PAH EWs that are half that of lower luminosity starbursts. A significant fraction (~40%-60%) of H II-like, LINER-like, and cold ULIRGs have very weak PAH EWs. Many of these ULIRGs also have large (τ9.7 > 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EW, but not with silicate optical depth. In addition, the PAH EW decreases with increasing rest-frame 24 μm luminosity. We argue that this trend results primarily from dilution of the PAH EW by continuum emission from dust heated by a compact central source, probably an AGN. High-luminosity, high-redshift sources studied with Spitzer appear to have a much larger range in PAH EW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs.The Astrophysical Journal 12/2008; 669(2):810. · 6.02 Impact Factor -
Article: Subarcsecond Resolution Mid-Infrared Observations of Super Star Clusters in the Antennae (NGC 4038/4039)
[show abstract] [hide abstract]
ABSTRACT: We present ground-based subarcsecond mid-infrared imaging and spectroscopy of young super star clusters in the overlap region of the merging galaxies NGC 4038/4039 (the Antennae) obtained with the VLT Imager and Spectrometer for mid-InfraRed (VISIR). With its unprecedented spatial resolution, VISIR begins for the first time to resolve the H II/photodissociation region complexes around the star-forming regions. In the N-band spectra of two young star clusters, unexpectedly low polycyclic aromatic hydrocarbon (PAH) emission is observed, compared to what is seen with the Infrared Space Observatory and with the Spitzer Space Telescope. We conclude that a large fraction of the PAH emission cannot be directly associated with the super star clusters but originates from an extended region of at least 215 pc radius around the clusters. In the distribution of [Ne II] 12.81 μm emission, a highly obscured cluster is discovered that does not have an optical or near-infrared counterpart.The Astrophysical Journal 12/2008; 648(1):L25. · 6.02 Impact Factor -
Article: Spitzer Infrared Spectrograph (IRS) Observations of the Redshift 3.91 Quasar APM 08279+5255
[show abstract] [hide abstract]
ABSTRACT: The Infrared Spectrograph (IRS) on board the Spitzer Space Telescope has been used to obtain low- and moderate-resolution spectra of the dust- and gas-rich quasar APM 08279+5255 (z = 3.91). Broad Paα and Paβ recombination lines of hydrogen were detected at wavelengths of 9.235 and 6.315 μm, respectively, as well as a strong, red continuum that is a smooth power law over the observed (rest-frame) wavelength range 5.3-35 μm (1.08-7.1 μm). The observed Paα/Paβ line flux ratio of 1.05 ± 0.2 is far from the case B value of ~2 and simple models of high-density, high optical depth ionized-gas regions (~1.8). This deviation is opposite in sense to the expected effect of reddening. No evidence is found in the spectrum for either the 3.3 or the 6.2 μm emission features usually attributed to aromatic hydrocarbons in gas-rich galaxies in the local universe. This is consistent with the high-luminosity active galactic nucleus (AGN) nature of APM 08279+5255.The Astrophysical Journal Supplement Series 12/2008; 154(1):151. · 13.46 Impact Factor -
Article: The Infrared Spectrograph (IRS) on the Spitzer Space Telescope
[show abstract] [hide abstract]
ABSTRACT: The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R = λ/Δλ ≈ 90 and 600, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the prelaunch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data-reduction pipeline has been developed at the Spitzer Science Center.The Astrophysical Journal Supplement Series 12/2008; 154(1):18. · 13.46 Impact Factor -
Article: Imaging of High-Redshift Submillimeter Galaxies at 16 and 22 microns with the Spitzer Infrared Spectrograph (IRS) Peak-up Cameras: Revealing a population at z > 2.5
[show abstract] [hide abstract]
ABSTRACT: We present broadband imaging observations obtained with the "peak-up" imagers of the Spitzer Space Telescope Infrared Spectrograph at wavelengths of 16 and 22 μm for a number of sources detected primarily at submillimeter wavelengths, which are believed to be at high, albeit undetermined, redshift. We targeted 11 sources originally detected by SCUBA and five submillimeter sources detected at 1.2 mm by MAMBO. Two optically discovered quasars with z > 6 were also observed to determine whether there is detectable dust emission at such high redshifts. Seven of the submillimeter sources and both high-redshift quasars were detected, and upper limits of about ~50 μJy apply to the remainder. Using their mid-/far-IR colors, we demonstrate that all of the submillimeter sources are at z > 1.4. The mid-IR colors for two of our detections and three of our strong upper limits suggest that these galaxies must be at z > 2.5. We also introduce a technique for estimating redshifts and source characteristics based only on the ratio of fluxes in the 16 and 22 μm images.The Astrophysical Journal Supplement Series 12/2008; 154(1):142. · 13.46 Impact Factor -
Article: The State of Protoplanetary Material 10 Million years after Stellar Formation: Circumstellar Disks in the TW Hydrae Association
[show abstract] [hide abstract]
ABSTRACT: We have used the Spitzer Space Telescope Infrared Spectrograph to observe seven members of the TW Hya association, the nearest stellar association whose age (~10 Myr) is similar to the timescales thought to apply to planet formation and disk dissipation. Only two of the seven targets display infrared excess emission, indicating that substantial amounts of dust still exist closer to the stars than is characteristic of debris disks; however, in both objects we confirm an abrupt short-wavelength edge to the excess, as is seen in disks with cleared-out central regions. The mid-infrared excesses in the spectra of Hen 3-600 and TW Hya include crystalline silicate emission features, indicating that the grains have undergone significant thermal processing. We offer a detailed comparison between the spectra of TW Hya and Hen 3-600, and a model that corroborates the spectral shape and our previous understanding of the radial structure of these protoplanetary disks.The Astrophysical Journal Supplement Series 12/2008; 154(1):439. · 13.46 Impact Factor
Top co-authors
Top Journals
Institutions
-
2008–2012
-
Universiteit Leiden
- Leiden Observartory
Leiden, South Holland, Netherlands -
Cornell University
- Department of Astronomy
Ithaca, NY, USA
-
