35 research outputs found
Towards an Understanding of the Mid-Infrared Surface Brightness of Normal Galaxies
We report a mid-infrared color and surface brightness analysis of IC 10, NGC
1313, and NGC 6946, three of the nearby galaxies studied under the Infrared
Space Observatory Key Project on Normal Galaxies. Images with < 9 arcsecond
(170 pc) resolution of these nearly face-on, late-type galaxies were obtained
using the LW2 (6.75 mu) and LW3 (15 mu) ISOCAM filters. Though their global
I_nu(6.75 mu)/I_nu(15 mu) flux ratios are similar and typical of normal
galaxies, they show distinct trends of this color ratio with mid-infrared
surface brightness. We find that I_nu(6.75 mu)/I_nu(15 mu) ~< 1 only occurs for
regions of intense heating activity where the continuum rises at 15 micron and
where PAH destruction can play an important role. The shape of the
color-surface brightness trend also appears to depend, to the second-order, on
the hardness of the ionizing radiation. We discuss these findings in the
context of a two-component model for the phases of the interstellar medium and
suggest that star formation intensity is largely responsible for the
mid-infrared surface brightness and colors within normal galaxies, whereas
differences in dust column density are the primary drivers of variations in the
mid-infrared surface brightness between the disks of normal galaxies.Comment: 19 pages, 6 figures, uses AAS LaTeX; to appear in the November
Astronomical Journa
The Interstellar Medium of Star-forming Irregular Galaxies: The View with ISO
We present mid-infrared imaging and far-infrared (FIR) spectroscopy of 5 IBm
galaxies observed by ISO as part of our larger study of the inter- stellar
medium of galaxies. Most of the irregulars in our sample are very actively
forming stars. The mid-infrared imaging was in a band centered at 6.75 microns
that is dominated by polycyclic aromatic hydrocarbons (PAHs) and in a band
centered at 15 microns that is dominated by small dust grains. The spectroscopy
of 3 of the galaxies includes [CII]158 microns and [OI]63 microns, important
coolants of photodissociation regions (PDRs), and [OIII]88 microns and [NII]122
microns, which come from ionized gas. [OI]145 microns and [OIII]52 microns were
measured in one galaxy as well. These data are combined with PDR and HII region
models to deduce properties of the interstellar medium of these galaxies.Comment: To be published in ApJ, Apr 10, 2001; higher resolution figures
available from ftp.lowell.edu, cd pub/dah/isopaper
Infrared Emission of Normal Galaxies from 2.5 to 12 Microns: ISO Spectra, Near-Infrared Continuum and Mid-Infrared Emission Features
We present ISO-PHOT spectra of the regions 2.5-4.9um and 5.8-11.6um for a
sample of 45 disk galaxies from the U.S. ISO Key Project on Normal Galaxies.
The spectra can be decomposed into three spectral components: (1) continuum
emission from stellar photospheres, which dominates the near-infrared (2.5-
4.9um; NIR) spectral region; (2) a weak NIR excess continuum, which has a color
temperature of ~ 1000K, carries a luminosity of a few percent of the total
far-infrared luminosity L(FIR), and most likely arises from the ISM; and (3)
the well-known broad emission features at 6.2, 7.7, 8.6 and 11.3 um, which are
generally attributed to aromatic carbon particles. These aromatic features in
emission (AFEs) dominate the mid-infrared (5.8-11.6 um; MIR) part of the
spectrum, and resemble the so-called Type-A spectra observed in many
non-stellar sources and the diffuse ISM in our own Galaxy. The relative
strengths of the AFEs vary by 15-25% among the galaxies. However, little
correlation is seen between these variations and either IRAS 60um-to-100um flux
density ratio R(60/100) or the FIR-to-blue luminosity ratio L(FIR)/L(B),
suggesting that the observed variations are not a direct consequence of the
radiation field differences among the galaxies. We demonstrate that the NIR
excess continuum and AFE emission are correlated, suggesting that they are
produced by similar mechanisms and similar (or the same) material. On the other
hand, as the current star-formation activity increases, the overall strengths
of the AFEs and the NIR excess continuum drop significantly with respect to
that of the far-infrared emission from large dust grains. This is likely a
consequence of the preferential destruction in intense radiation fields of the
small carriers responsible for the NIR/AFE emission.Comment: With 8 tables and 12 figures; to appear in the Astrophysical Journa
VizieR Online Data Catalog: SN 2011dh. The first two years (Ergon+, 2015)
All data for the first 100 days (from Paper I, Ergon et al., 2014A&A...562A..17E) and JC UBVRI, SDSS ugriz and 2MASS JHK magnitudes after day 100 and pseudo-bolometric UV-MIR bolometric luminosity before day 400 for SN 2011dh. (4 data files)