Joseph B. Jensen

GOALS: The Great Observatories All-Sky LIRG Survey

ABSTRACT.The Great Observatories All-Sky LIRG Survey (GOALS20) combines data from NASA’s Spitzer Space Telescope, Chandra X-Ray Observatory, Hubble Space Telescope (HST), and Galaxy Evolution Explorer (GALEX) observatories, together with ground-based data, into a comprehensive imaging and spectroscopic survey of over 200 low-redshift (zxa0<xa00.088z<0.088), Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of the IRAS Revised Bright Galaxy Sample (RBGS), which comprises 629 extragalactic objects with 60xa0μm flux densities above 5.24xa0Jy, and Galactic latitudes above five degrees. The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams (type-1 and type-2 AGN, LINERs, and starbursts) as well as interaction stages (major mergers, minor mergers, and isolated galaxies). They provide an unbiased picture of the processes responsible for enhanced infrared emission in galaxies in the local Universe. As an example of the analytic powe...

The Brightest Stars in M32: Comparing Predictions from Spectra with the Resolved Stellar Content

Broadband and narrowband images covering the 1-4 μm wavelength interval are used to investigate the properties of the brightest asymptotic giant branch (AGB) stars in the Local Group galaxy M32. Data obtained with the NIRI imager on the Gemini North telescope indicate that the brightest AGB stars near the center of M32 have peak M brightnesses and K - L colors that are similar to those of luminous AGB stars in the Galactic disk. Data obtained with the CFHTIR imager on the Canada-France-Hawaii Telescope indicate that the density of bright AGB stars per unit visible and near-infrared surface brightness is constant out to projected major-axis distances of 1 kpc, suggesting that the AGB stars and their progenitors are smoothly mixed throughout the main body of the galaxy. In addition, the J - K color distribution of bright AGB stars throughout much of the galaxy is consistent with that of a single population of AGB stars, the majority of which are long-period variables that have a common metallicity and age. Thus, these data do not support spectroscopic studies that find an age gradient in M32. The AGB contributes 70% of the integrated light in the region surveyed. This is consistent with previous estimates made from the integrated near-infrared spectrum and is suggestive of an age of ~2 Gyr. The stellar content of M32 is compared with that of the M31 bulge at a projected minor-axis distance of 1.4 kpc. While the peak K-band brightnesses of AGB stars in the two systems agree to within a few tenths of a magnitude, M32 contains more bright AGB stars per unit integrated brightness than the outer bulge of M31. This suggests a difference in mean age, and it is concluded that the star-forming histories of M32 and the bulge of M31 have differed over a significant fraction of their lifetimes, which is consistent with spectroscopic studies of these systems. The well-mixed AGB content of M32 is consistent with the galaxy having been tidally stirred, presumably by interactions with M31.

Tracing Polycyclic Aromatic Hydrocarbons and Warm Dust Emission in the Seyfert Galaxy NGC 1068

We present a study of the nearby Seyfert galaxy NGC 1068 using mid- and far-infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the Spitzer Space Telescope. The images show extensive 8 and 24 μm emission coinciding with star formation in the inner spiral approximately 15 (1 kpc) from the nucleus and a bright complex of star formation ~47 (3 kpc) southwest of the nucleus. The brightest 8 μm polycyclic aromatic hydrocarbon (PAH) emission regions coincide remarkably well with knots observed in an Hα image. Strong PAH features at 6.2, 7.7, 8.6, and 11.3 μm are detected in IRS spectra measured at numerous locations inside, within, and outside the inner spiral. The IRAC colors and IRS spectra of these regions rule out dust heated by the active galactic nucleus (AGN) as the primary emission source; the spectral energy distributions are dominated by starlight and PAH emission. The equivalent widths and flux ratios of the PAH features in the inner spiral are generally consistent with conditions in a typical spiral galaxy interstellar medium (ISM). Interior to the inner spiral, the influence of the AGN on the ISM is evident via PAH flux ratios indicative of a higher ionization parameter and a significantly smaller mean equivalent width than observed in the inner spiral. The brightest 8 and 24 μm emission peaks in the disk of the galaxy, even at distances beyond the inner spiral, are located within the ionization cones traced by [O III]/Hβ, and they are also remarkably well aligned with the axis of the radio jets. Although it is possible that radiation from the AGN may directly enhance PAH excitation or trigger the formation of OB stars that subsequently excite PAH emission at these locations in the inner spiral, the orientation of collimated radiation from the AGN and star formation knots in the inner spiral could be coincidental. The brightest PAH- and 24 μm-emitting regions are also located precisely where two spiral arms of molecular gas emerge from the ends of the inner stellar bar; this is consistent with kinematic models that predict maxima in the accumulation and compression of the ISM, where gas gets trapped within the inner Lindblad resonance of a large stellar bar that contains a smaller, weaker bar.

The Central Regions of M31 in the 3-5 μm Wavelength Region*

Images obtained with NIRI on the Gemini North telescope are used to investigate the photometric properties of the central regions of M31 in the 3-5 μm wavelength range. The light distribution in the central arcsecond differs from what is seen in the near-infrared in the sense that the difference in peak brightness between P1 and P2 is larger in M than in K; no obvious signature of P3 is detected in M. These results can be explained if there is a source of emission that contributes ~20% of the peak M light of P1, has an effective temperature of no more than a few hundred K, and is located between P1 and P2. Based on the red K - M color of this source, it is suggested that the emission originates in a circumstellar dust shell surrounding a single bright asymptotic giant branch (AGB) star. Tests of this hypothesis are described. A bright source that is ~8 from the center of the galaxy is also detected in M. This object has red colors and an absolute brightness in M that is similar to the most highly evolved AGB stars in the solar neighborhood; hence, it is likely to be a very evolved AGB star embedded in a circumstellar envelope. The K-band brightness of this star is close to the peak expected for AGB evolution, and an age of only a few hundred million years is estimated, which is comparable to that of the P3 star cluster. Finally, using high angular resolution near-infrared adaptive optics images as a guide, a sample of unblended AGB stars outside of the central few arcseconds is defined in L. The (L, K - L) color-magnitude diagram of these sources shows a dominant AGB population with a peak L brightness and a range of K - L colors that are similar to those of the most luminous M giants in the Galactic bulge.

The infrared universe: The cosmic evolution of superstarbursts and massive black holes

Our view of galaxy evolution has been dramatically enhanced by recent deep field surveys at far-infrared and submillimeter wavelengths. Current evidence suggests that the number density of the most luminous far-infrared sources evolves strongly with redshift, and that the nluminosity density in the far-infrared/submillimeter may exceed that in the optical/ultraviolet by factors of 3 − 10 at redshifts z > 1. If true, then as much as 80-90% of the “activity” in galaxies at z > 1 may be hidden by dust. Surveys of complete samples of luminous infrared galaxies in the local Universe show that the majority, if not all objects with log (L_(ir)/L_☉) ≳ 11.6, appear to be major mergers of molecular gas-rich disks accompanied by dust-enshrouded nuclear starbursts and powerful AGN. If the majority of the deep-field sources are simply more ndistant analogs of local luminous infrared galaxies, then we may be witnessing at z ~ 1 − 3 the primary epoch in the formation of spheroids and massive black holes. This major event in galaxy evolution is largely missed by current deep optical/ultraviolet surveys.