Dust Abundance and Properties in the Nearby Dwarf Galaxies NGC 147 and NGC 185

We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185, and NGC 147, obtained with the Spitzer Space Telescope. Spitzer's high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 μm display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50" but beyond this radius, the 160 μm emission is more extended than that at 24 and 70 μm. On the other hand, the dwarf galaxy NGC 147, located only a small distance away from NGC 185, shows no significant infrared emission beyond 24 μm and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9 × 10^3 M_⊙, implying a gas mass of 3.0 × 10^5 M_⊙. These values are in agreement with those previously estimated from infrared as well as CO and H I observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation 1 × 10^9 yr ago. Based on the 70-160 μm flux density ratio, we estimate a temperature for the dust of ~17 K. For NGC 147, we obtain an upper limit for the dust mass of 4.5 × 10^2 M_⊙ at 160 μm (assuming a temperature of ~20 K), a value consistent with the previous upper limit derived using Infrared Space Observatory observations of this galaxy. In the case of NGC 185, we also present full 5-38 μm low-resolution (R ~ 100) spectra of the main emission regions. The Infrared Spectrograph spectra of NGC 185 show strong polycyclic aromatic hydrocarbons emission, deep silicate absorption features and H_2 pure rotational line ratios consistent with having the dust and molecular gas inside the dust cloud being impinged by the far-ultraviolet radiation field of a relatively young stellar population. Therefore, based on its infrared spectral properties, NGC 185 shows signatures of recent star formation (a few ×10^8 yr ago), although its current star formation rate is quite low

The Balloon-Borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 10 deg^2 Survey of Star Formation in Cygnus X

We present Cygnus X in a new multi-wavelength perspective based on an unbiased BLAST survey at 250, 350, and 500 μm, combined with rich data sets for this well-studied region. Our primary goal is to investigate the early stages of high-mass star formation. We have detected 184 compact sources in various stages of evolution across all three BLAST bands. From their well-constrained spectral energy distributions, we obtain the physical properties mass, surface density, bolometric luminosity, and dust temperature. Some of the bright sources reaching 40 K contain well-known compact H_(II) regions. We relate these to other sources at earlier stages of evolution via the energetics as deduced from their position in the luminosity-mass (L-M) diagram. The BLAST spectral coverage, near the peak of the spectral energy distribution of the dust, reveals fainter sources too cool (~10 K) to be seen by earlier shorter-wavelength surveys like IRAS. We detect thermal emission from infrared dark clouds and investigate the phenomenon of cold "starless cores" more generally. Spitzer images of these cold sources often show stellar nurseries, but these potential sites for massive star formation are "starless" in the sense that to date there is no massive protostar in a vigorous accretion phase. We discuss evolution in the context of the L-M diagram. Theory raises some interesting possibilities: some cold massive compact sources might never form a cluster containing massive stars, and clusters with massive stars might not have an identifiable compact cold massive precursor

Optical and Infrared Photometry of the Type Ia Supernovae 1991T, 1991bg, 1999ek, 2001bt, 2001cn, 2001cz, and 2002bo

We present optical and/or infrared photometry of the Type Ia supernovae SN 1991T, SN 1991bg, SN 1999ek, SN 2001bt, SN 2001cn, SN 2001cz, and SN 2002bo. All but one of these supernovae have decline rate parameters, Δm_(15)(B), close to the median value of 1.1 for the whole class of Type Ia supernovae. The addition of these supernovae to the relationship between the near-infrared absolute magnitudes and Δm_(15)(B) strengthens the previous relationships we have found in that the maximum light absolute magnitudes are essentially independent of the decline rate parameter. (SN 1991bg, the prototype of the subclass of fast-declining Type Ia supernovae, is a special case.) The dispersion in the Hubble diagram in JHK is only ~0.15 mag. The near-infrared properties of Type Ia supernovae continue to be excellent measures of the luminosity distances to the supernova host galaxies because of the need for only small corrections from the epoch of observation to maximum light, low dispersion in absolute magnitudes at maximum light, and the minimal reddening effects in the near-infrared

A Direct Measurement of the Dust Extinction Curve in an Intermediate-Redshift Galaxy

We present a proof-of-concept study that dust extinction curves can be extracted from the infrared (IR), optical, ultraviolet (UV) and X-ray afterglow observations of GRBs without assuming known extinction laws. We focus on GRB 050525A (z = 0.606), for which we also present IR observations from the Spitzer Space Telescope at about 2.3 days post-burst. We construct the spectral energy distribution (SED) of the afterglow and use it to derive the dust extinction curve of the host galaxy in 7 optical/UV wavebands. By comparing our derived extinction curve to known templates, we see that the Galactic or Milky Way extinction laws are disfavored versus the Small and Large Magellanic Cloud (SMC and LMC) ones, but that we cannot rule out the presence of a LMC-like 2175 angstrom bump in our extinction curve. The dust-to-gas ratio present within the host galaxy of GRB 050525A is similar to that found in the LMC, while about 10 to 40% more dust is required if the SMC template is assumed. Our method is useful to observatories that are capable of simultaneously observing GRB afterglows in multiple wavebands from the IR to the X-ray.Comment: 9 pages, 5 figures. Accepted by ApJ. Minor changes to 2nd Paragraph of Introductio

The Optical Proper Motions of HH 7-11 and Cep E (HH 377)

A key ingredient in understanding the dynamics of stellar outflows is their proper motion. We have used optical images in the [SII] emission at 6717/31 A and the red Digitized Palomar Observatory Sky Survey (DSS) plates to determine the proper motion of HH 7-11 system and the optical knot of Cep E (HH 377). The DSS plate measurements span nearly 37 years for both HH 7-11 and HH 377 and have wide field of view, which allows an accurate determination of the proper motions despite their relatively low angular resolution. The optical images, with higher angular resolution, cover a shorter period of 7 and 4 years, respectively, and have been used to complement the DSS measurements. From the DSS plates we have found that HH 377 has a proper motion of 0.031 +/- 0.003 arcsec/yr with a PA = 206 arcdeg, i.e. moving away from IRAS 230111+63, that at a distance of 730 pc corresponds to a tangential velocity of 107 +/- 14 km/s. The values obtained from the optical images are consistent with these measurements. Similarly, the proper motions of HH 7-11 range from 0.015 +/- 0.009 (HH 9) to 0.044 +/- 0.007 (HH 11) arcsec/yr, and the flow is moving away from SVS 13 with a mean PA = 136 arcdeg. At a distance of 330 pc, these motions correspond to tangential velocities of 25 - 70 km/s, i.e. comparable to the original values obtained by Herbig & Jones (1983). The measurements from the optical CCD [SII] images are again consistent with these motions, although in detail there are some difference, particularly for HH 7 and HH 10.Comment: 18 pages, 6 Figures (jpgs because of their size