24 research outputs found
Flame: A Flexible Data Reduction Pipeline for Near-Infrared and Optical Spectroscopy
We present flame, a pipeline for reducing spectroscopic observations obtained
with multi-slit near-infrared and optical instruments. Because of its flexible
design, flame can be easily applied to data obtained with a wide variety of
spectrographs. The flexibility is due to a modular architecture, which allows
changes and customizations to the pipeline, and relegates the
instrument-specific parts to a single module. At the core of the data reduction
is the transformation from observed pixel coordinates (x, y) to rectified
coordinates (lambda, gamma). This transformation consists in the polynomial
functions lambda(x,y) and gamma(x,y) that are derived from arc or sky emission
lines and slit edge tracing, respectively. The use of 2D transformations allows
one to wavelength calibrate and rectify the data using just one interpolation
step. Furthermore, the gamma(x,y) transformation includes also the spatial
misalignment between frames, which can be measured from a reference star
observed simultaneously with the science targets. The misalignment can then be
fully corrected during the rectification, without having to further resample
the data. Sky subtraction can be performed via nodding and/or modeling of the
sky spectrum; the combination of the two methods typically yields the best
results. We illustrate the pipeline by showing examples of data reduction for a
near-infrared instrument (LUCI at the Large Binocular Telescope) and an optical
one (LRIS at the Keck telescope).Comment: 17 pages, 10 figures, published in MNRAS. The pipeline is available
at https://github.com/siriobelli/flam
Uncovering the Active Galactic Nuclei in Low-Ionization Nuclear Emission-Line Regions with Spitzer
The impact of active galactic nuclei on low-ionization nuclear emission-line
regions (LINERs) remains a vigorous field of study. We present preliminary
results from a study of the mid-infrared atomic emission lines of LINERs with
the Spitzer Space Telescope. We assess the ubiquity and properties of AGN in
LINERs using this data. We discuss what powers the mid-infrared emission lines
and conclude that the answer depends unsurprisingly on the emission line
ionization state and, more interestingly, on the infrared luminosity.Comment: To appear in ASP Vol. 373, The Central Engine of Active Galactic
Nuclei, ed. Luis C. Ho and Jian-Min Wang; 4 pages, 2 figure
The star formation properties of disk galaxies: Halpha imaging of galaxies in the Coma supercluster
We present integrated H alpha measurements obtained from imaging observations
of 98 late-type galaxies, primarily selected in the Coma supercluster. These
data, combined with H alpha photometry from the literature, include a magnitude
selected sample of spiral (Sa to Irr) galaxies belonging to the "Great Wall"
complete up to mp=15.4, thus composed of galaxies brighter than Mp=-18.8
(H0=100 km Mpc^-1 s^-1). The frequency distribution of the H alpha E.W.,
determined for the first time from an optically complete sample, is
approximately gaussian peaking at E.W. ~25 A. We find that, at the present
limiting luminosity, the star formation properties of spiral+Irr galaxies
members of the Coma and A1367 clusters do not differ significantly from those
of the isolated ones belonging to the Great Wall. The present analysis confirms
the well known increase of the current massive star formation rate (SFR) with
Hubble type. Moreover perhaps a more fundamental anticorrelation exists between
the SFR and the mass of disk galaxies: low-mass spirals and dwarf systems have
present SFRs ~50 times higher than giant spirals. This result is consistent
with the idea that disk galaxies are coeval, evolve as "closed systems" with
exponentially declining SFR and that the mass of their progenitor protogalaxies
is the principal parameter governing their evolution. Massive systems having
high initial efficiency of collapse, or a short collapse time-scale, have
retained little gas to feed the present epoch of star formation. These findings
support the conclusions of Gavazzi & Scodeggio (1996) who studyed the
color-mass relation of a local galaxy sample and agree with the analysis by
Cowie et al. (1996) who traced the star formation history of galaxies up to
z>1.Comment: 13 pages (LateX) + 24 figures + 4 tables. To appear in Astronomical
Journal, April 1998 issu
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
Spitzer Quasar and ULIRG Evolution Study (QUEST). II. The Spectral Energy Distributions of Palomar-Green Quasars
This is the second paper studying the QSOs in the Spitzer QUEST sample. Previously we presented new PAH measurements and argued that most of the observed far-infrared (FIR) radiation is due to star-forming activity. Here we present spectral energy distributions (SEDs) by supplementing our data with optical, NIR, and FIR observations. We define two subgroups, of "weak FIR" and "strong FIR" QSOs, and a third group of FIR nondetections. Assuming a starburst origin for the FIR, we obtain "intrinsic" active galactic nucleus (AGN) SEDs by subtracting a starburst template from the mean SEDs. The resulting SEDs are remarkably similar for all groups. They show three distinct peaks corresponding to two silicate emission features and a 3 μm bump, which we interpret as the signature of the hottest AGN dust. They also display drops beyond ~20 μm that we interpret as the signature of the minimum temperature (~200 K) dust. This component must be optically thin to explain the silicate emission and the slope of the long-wavelength continuum. We discuss the merits of an alternative model in which most of the FIR emission is due to AGN heating. Such models are unlikely to explain the properties of our QSOs, but they cannot be ruled out for more luminous objects. We also find correlations between the luminosity at 5100 Å and two infrared starburst indicators: L(60 μm) and L(PAH 7.7 μm). The correlation of L(5100 Å) with L(60 μm) can be used to measure the relative growth rates and lifetimes of the black hole and the new stars
ISO--LWS observations of the two nearby spiral galaxies: NGC6946 and NGC1313
(Abridged) We present the analysis of the main FIR fine structure lines
emission in NGC1313 and NGC6946. We calculate that a component probably
associated with the diffuse disks contributes <~40% in N6946 and ~30 % in N1313
to the total [CII] emission. The main PDR physical parameters responsible for
the neutral atomic gas emission in N1313 and N6946 do not significantly differ
from what Malhotra etal (2001) found by modelling the integrated emission of a
sample of 60 normal galaxies,although there are evidences for a beam averaged
contribution of a less active component inside NGC6946 higher than its
contribution in the integrated emission of normal galaxies. CO and [CII] in
N6946 are well correlated with a mean [CII]/CO ratio similar to that of the
normal galaxies sample. In N1313 the [CII]/CO seems to systematically increase
from the North to the south, along the S-shaped spiral arm, indicating much
more inhomogeneous conditions than in N6946. HI and [CII] in N6946 are
completely de-correlated, probably because they arise from different gas
components. In N1313 we successfully detect two distinct gas components: a
cirrus-like component where HI and [CII] are weakly correlated as observed in
our Galaxy, and a component associated with dense PDRs completely de-correlated
from HI as observed in N6946.Finally, we find that the HI residing in dense
PDRs and presumably recently photo-dissociated, constitutes a few % of the
total HI. In turn, this dense gas component produces most of the [CII] emission
emitted by the atomic neutral medium.Comment: Latex, 100 pages, 11 Figures, 11 Tables. Accepted for publication in
A
The elusive ISM of dwarf galaxies: excess submillimetre emission & CO-dark molecular gas
The Herschel Dwarf Galaxy Survey investigates the interplay of star formation activity and the the metal-poor gas and dust of dwarf galaxies using FIR and submillimetre imaging spectroscopic and photometric observations in the 50 to 550mu window of the Herschel Space Observatory. The dust SEDs are well constrained with the new Herschel and MIR Spitzer data. A submillimetre excess is often found in low metallicity galaxies, which,if tracing very cold dust, would highlight large dust masses not easily reconciled in some cases, given the low metallicities and expected gas-to-dust mass ratios. The galaxies are also mapped in the FIR fine-structure lines (63 and 145mu OI, 158mu CII, 122 and 205mu NII, 88mu OIII) probing the low density ionised gas, the HII regions and photodissociation regions. While still early in the Herschel mission we can already see, along with earlier studies, that line ratios in the metal-poor ISM differ remarkably from those in the metal-rich starburst environments. In dwarf galaxies, L[CII]/L(CO) (>10^4) is at least an order of magnitude greater than in the most metal-rich starburst galaxies. The enhanced [CII] arises from the larger photodissociation region where H2, not traced by the CO, can exist. The 88mu [OIII] line usually dominates the FIR line emission over galaxy-wide scales in dwarf galaxies, not the 158mu [CII] line which is the dominant FIR cooling line in metal-rich galaxies. All of the FIR lines together can contribute 1% to 2% of the L(TIR). The Herschel Dwarf Galaxy survey will provide statistical information on the nature of the dust and gas in low metallicity galaxies, elucidating the origin of the submm excess in dwarf galaxies, and help determine a ([CII] +CO) to H2 conversion factor, thus providing observational constraints on chemical evolution models of galaxies
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