29 research outputs found
PAH Emission from Ultraluminous Infrared Galaxies
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 within a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 µm PAH equivalent widths (EQWs) in the sample span more than two orders of magnitude (∼0.006–0.8 µm), and ULIRGs with HII-like optical spectra or steep far-infrared spectral slopes (S25/S60 \u3c 0.2) typically have 6.2 µm PAH EQWs that are half that of lower-luminosity starbursts. A significant fraction (∼40–60%) of HII-like, LINER-like, and cold ULIRGs have very weak PAH EQWs. Many of these ULIRGs also have large (τ9.7 \u3e 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EQW, but not with silicate optical depth. In addition, the PAH EQW decreases with increasing rest-frame 24 µm luminosity. We argue that this trend results primarily from dilution of the PAH EQW by continuum emission from dust heated by a compact central source, probably an AGN. High luminosity, highredshift sources studied with Spitzer appear to have a much larger range in PAH EQW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs
GOALS-JWST: hidden star formation and extended PAH emission in the luminous infrared galaxy VV 114
Galaxie
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
welcom
A new luminosity component in 3C 48
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Quasars measured by the Infrared Astronomical Satellite
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Near-Infrared Observations of the Extremely Red Object CL 0939+4713B: An Old Galaxy at Z~1.58?
Near infrared imaging and spectroscopic observations of the extremely red
object (R-K~ 7 mag) CL 0939+4713 B have been obtained with the Near Infrared
Camera on the Keck I Telescope of the W. M. Keck Observatory. The imaging shows
a slightly elongated structure, while the spectroscopy shows a continuum break
that allows us to determine the redshift of z = 1.58 + 0.01/-0.03 for this
system. The fits of a range of models to the infrared spectrum suggests that it
is predominantly an old (> 10^9 yrs) stellar system that suffers little
extinction, while the measurerd R and I magnitudes suggests an age of ~ 3 x
10^8 years. The limit on the equivalent width of any emission line in the
infrared spectrum argues that CL 0939+4713 B is not an actively star forming
galaxy. This system, though similar in R-K color to HR 10 [also known as
J1645+46] (Dey et al. 1999), is much different in morphology and emission line
strengths, demonstrating the heterogeneity of extremely red extragalactic
objects (EROs) selected on the basis of large values of R-K.Comment: Latex with AAS format, 3 postscript figures, AJ, accepted, includes
new I data, new fig 3 and revised interpretatio