89 research outputs found
Spectro-Morphology of Galaxies
We present a quantitative method to classify galaxies, based on
multi-wavelength data and elaborated from the properties of nearby galaxies.
Our objective is to define an evolutionary method that can be used for low and
high redshift objects. We estimate the concentration of light (C) at the galaxy
center and the 180 degree-rotational asymmetry (A), computed at several
wavelengths, from ultraviolet (UV) to I-band. The variation of the indices of
concentration and asymmetry with the wavelength reflects the proportion and the
distribution of young and old stellar populations in galaxies. In general C is
found to decrease from optical to UV, and A is found to increase from optical
to UV: the patchy appearance of galaxies in UV with no bulge is often very
different from their counterpart at optical wavelengths, with prominent bulges
and more regular disks. The variation of C and A with the wavelength is
quantified. By this way, we are able to distinguish five types of galaxies that
we call spectro-morphological types: compact, ringed, spiral, irregular and
central-starburst galaxies, which can be differentiated by the repartition of
their stellar populations. We discuss in detail the morphology of galaxies of
the sample, and describe the morphological characteristics of each
spectro-morphological type. We apply spectro-morphology to three objects at a
redshift z=1 in the Hubble Deep Field North, that gives encouraging results for
applications to large samples of high-redshift galaxies. This method of
morphological classification could be used to study the evolution of the
morphology with the redshift and is expected to bring observational constraints
on scenarios of galaxy evolution.Comment: Accepted for publication in Astronomy & Astrophysic
Discovery of a Boxy Peanut Shaped Bulge in the Near Infrared
We report on the discovery of a boxy/peanut shaped bulge in the highly
inclined barred Seyfert 2 galaxy NGC~7582. The peanut shape is clearly evident
in near infrared images but obscured by extinction from dust in visible
images. This suggests that near infrared imaging surveys will discover a
larger number of boxy/peanut morphologies than visible surveys, particularly in
galaxies with heavy extinction such as NGC~7582. The bulge in NGC~7582 exhibits
strong boxiness compared to other boxy/peanut shaped bulges. If the starburst
was mediated by the bar, then it is likely that the bar formed in less than a
few bar rotation periods or a few years ago. If the bar also
caused the peanut, then the peanut would have formed quickly; on a timescale of
a few bar rotation periods.Comment: AAS Latex and Postcript Figures, accepted for publication in Ap
V, J, H and K Imaging of the Metal Rich Globular Cluster NGC 6528
New near-infrared observations of NGC6528 are presented. The JHK observations
complement a previous HST/NICMOS data set by Ortolani et al. (2001), in that
they sample a larger area, contain a more numerous sample of red giant stars,
and include the K band. Also, archival HST data sets (separated by 6.093 years)
were used to proper-motion decontaminate the near-infrared sample and extract a
clean VJHK catalogue. Using the present wide colour baseline, we compared the
cleaned colour-magnitude diagrams of NGC6528 with those of NGC 6553 and NGC104
and derived new estimates of reddening and distance, E(B-V)=0.55 and
(m-M)o=14.44 (7.7 kpc). Moreover, the morphology and location of the cleaned
red giant branch were used to derive a photometric estimate of the cluster
metallicity. The average of 10 metallicity indicators yields a mean value of
[M/H] ~ 0.0, and [Fe/H] ~-0.20 and +0.08 on the Zinn & West (1984) and Carretta
& Gratton (1997) revised metallicity scale, respectively. The best isochrone
fit to the cleaned K,V-K diagram is obtained for a 12.6 Gyr and Z=0.02
isochrone, i.e. the derived metallicity of NGC6528 turns out to be very close
to the mean of stars in the Baade's Window. Five AGB variable star candidates,
whose membership has to be confirmed spectroscopically, are bolometrically as
bright as the known long period variable stars in NGC6553. As discussed in
Guarnieri et al. (1997) for NGC6553, this may indicate that an `intermediate
age' population is not needed to account for the brightest stars in external
galaxies such as M32.Comment: 11 pages, 9 figures, A&A accepte
The Frequency of Barred Spiral Galaxies in the Near-IR
We have determined the fraction of barred galaxies in the H-band for a
statistically well-defined sample of 186 spirals drawn from the Ohio State
University Bright Spiral Galaxy survey. We find 56% of our sample to be
strongly barred at H, while another 16% is weakly barred. Only 27% of our
sample is unbarred in the near-infrared. The RC3 and the Carnegie Atlas of
Galaxies both classify only about 30% of our sample as strongly barred. Thus
strong bars are nearly twice as prevalent in the near-infrared as in the
optical. The frequency of genuine optically hidden bars is significant, but
lower than many claims in the literature: 40% of the galaxies in our sample
that are classified as unbarred in the RC3 show evidence for a bar in the
H-band, while for the Carnegie Atlas this fraction is 66%. Our data reveal no
significant trend in bar fraction as a function of morphology in either the
optical or H-band. Optical surveys of high redshift galaxies may be strongly
biased against finding bars, as bars are increasingly difficult to detect at
bluer rest wavelengths.Comment: LaTeX with AASTeX style file, 23 pages with 6 figures. Accepted for
publication in The Astronomical Journal (Feb. 2000
Quantitative Morphology of Galaxies Observed in the Ultraviolet
We present a quantitative study of the far-ultraviolet (FUV) and optical
morphology in 32 nearby galaxies and estimate the ``morphological
k-correction'' expected if these objects were observed unevolved at high
redshift. Using the common indices of central concentration (C) and rotational
asymmetry (A) to quantify morphology, we consider independently two phenomena
that give rise to this k-correction. Bandshifting, the decrease in rest-frame
wavelength of light observed through optical filters, is explored by measuring
these indices in several passbands for each galaxy, and it is found to be the
primary driver of changes in C and A. In general, the optical trend found for
decreasing C and increasing A when going to shorter wavelengths extends to the
FUV. However, the patchy nature of recent star-formation in late-type galaxies,
which is accentuated in the FUV, results in poor quantitative correspondence
between morphologies determined in the optical and FUV. We then artificially
redshift our FUV images into the Hubble Deep Field (HDF) filters to simulate
various cosmological distance effects such as surface brightness dimming and
loss of spatial resolution. Hubble types of many galaxies in our sample are not
readily identifiable at redshifts beyond z ~ 1, and the galaxies themselves are
difficult to detect beyond z ~ 3. Only features of the highest surface
brightness remain visible at cosmological distances. Our simulations suggest
that k-corrections alone are indeed capable of producing the peculiar
morphologies observed at high redshift.Comment: accepted to the Astrophysical Journa
Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths
We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet
(FUV, ~1500A) and optical (UBVRI) passbands to characterize galaxy morphology
as a function of wavelength. This sample, which includes a range of classical
Hubble types from elliptical to irregular with emphasis on spirals at low
inclination angle, provides a valuable database for comparison with images of
high-z galaxies whose FUV light is redshifted into the optical and near-
infrared bands. Ultraviolet data are from the UIT Astro-2 mission. We present
images and surface brightness profiles for each galaxy, and we discuss the
wavelength-dependence of morphology for different Hubble types in the context
of understanding high-z objects. In general, the dominance of young stars in
the FUV produces the patchy appearance of a morphological type later than that
inferred from optical images. Prominent rings and circumnuclear star formation
regions are clearly evident in FUV images of spirals, while bulges, bars, and
old, red stellar disks are faint to invisible at these short wavelengths.
However, the magnitude of the change in apparent morphology ranges from
dramatic in early--type spirals with prominent optical bulges to slight in
late-type spirals and irregulars, in which young stars dominate both the UV and
optical emission. Starburst galaxies with centrally concentrated, symmetric
bursts display an apparent ``E/S0'' structure in the FUV, while starbursts
associated with rings or mergers produce a peculiar morphology. We briefly
discuss the inadequacy of the optically-defined Hubble sequence to describe FUV
galaxy images and estimate morphological k-corrections, and we suggest some
directions for future research with this dataset.Comment: Accepted for publication in the ApJS. 15 pages, 17 JPEG figures, 10
GIF figures. Paper and full resolution figures available at
http://nedwww.ipac.caltech.edu/level5/Kuchinski/frames.htm
High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters
Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle
spectra covering the 1.5-1.8 micron range for giant stars in the massive bulge
globular clusters NGC6440 and NGC6441. We report the first high dispersion
abundance for NGC6440, [Fe/H]=-0.56+/-0.02 and we find [Fe/H]=-0.50+/-0.02 for
the blue HB cluster NGC6441. We measure an average -enhancement of
~+0.3 dex in both clusters, consistent with previous measurements of other
metal rich bulge clusters, and favoring the scenario of a rapid bulge formation
and chemical enrichment. We also measure very low 12C/13C isotopic ratios
(~5+/- 1), suggesting that extra-mixing mechanisms are at work during evolution
along the Red Giant Branch also in the high metallicity regime. We also measure
Al abundances, finding average [Al/Fe]=0.45+/-0.02 and [Al/Fe]=0.52+/-0.02 in
NGC6440 and NGC6441, respectively, and some Mg-Al anti-correlation in NGC6441.
We also measure radial velocities vr=-76+/-3 km/s and vr=+14+/-3 km/s and
velocity dispersions sigma=9+/-2 km/s and sigma=10+/-2 km/s, in NGC6440 and
NGC6441, respectively.Comment: 8 pages, 7 figure
Two Interacting Electrons in a Quasiperiodic Chain
We study numerically the effect of on-site Hubbard interaction U between two
electrons in the quasiperiodic Harper's equation. In the periodic chain limit
by mapping the problem to that of one electron in two dimensions with a
diagonal line of impurities of strength U we demonstrate a band of resonance
two particle pairing states starting from E=U. In the ballistic (metallic)
regime we show explicitly interaction-assisted extended pairing states and
multifractal pairing states in the diffusive (critical) regime. We also obtain
localized pairing states in the gaps and the created subband due to U, whose
number increases when going to the localized regime, which are responsible for
reducing the velocity and the diffusion coefficient in the qualitatively
similar to the non-interacting case ballistic and diffusive dynamics. In the
localized regime we find propagation enhancement for small U and stronger
localization for larger U, as in disordered systems.Comment: 14 pages Revtex file, 8 figures (split into 19 jpg figures).
(postscript versions of the jpg figures are also available upon request)
submitted to PR
A New Non-Parametric Approach to Galaxy Morphological Classification
We present two new non-parametric methods for quantifying galaxy morphology:
the relative distribution of the galaxy pixel flux values (the Gini coefficient
or G) and the second-order moment of the brightest 20% of the galaxy's flux
(M20). We test the robustness of G and M20 to decreasing signal-to-noise and
spatial resolution, and find that both measures are reliable to within 10% at
average signal-to-noise per pixel greater than 3 and resolutions better than
1000 pc and 500 pc, respectively. We have measured G and M20, as well as
concentration (C), asymmetry (A), and clumpiness (S) in the rest-frame
near-ultraviolet/optical wavelengths for 150 bright local "normal" Hubble type
galaxies (E-Sd) galaxies and 104 0.05 < z < 0.25 ultra-luminous infrared
galaxies (ULIRGs).We find that most local galaxies follow a tight sequence in
G-M20-C, where early-types have high G and C and low M20 and late-type spirals
have lower G and C and higher M20. The majority of ULIRGs lie above the normal
galaxy G-M20 sequence, due to their high G and M20 values. Their high Gini
coefficients arise from very bright nuclei, while the high second-order moments
are produced by multiple nuclei and bright tidal tails. All of these features
are signatures of recent and on-going mergers and interactions. We also find
that in combination with A and S, G is more effective than C at distinguishing
ULIRGs from the "normal" Hubble-types. Finally, we measure the morphologies of
45 1.7 < z < 3.8 galaxies from HST NICMOS observations of the Hubble Deep Field
North. We find that many of the z 2 galaxies possess G and A higher than
expected from degraded images of local elliptical and spiral galaxies, and have
morphologies more like low-redshift single nucleus ULIRGs.Comment: 48 pages, 9 tables and 17 figures, accepted to the Astronomical
Journal with minor revision
The Galaxy Structure-Redshift Relationship
There exists a gradual, but persistent, evolutionary effect in the galaxy
population such that galaxy structure and morphology change with redshift. This
galaxy structure-redshift relationship is such that an increasingly large
fraction of all bright and massive galaxies at redshifts 2 < z < 3 are
morphologically peculiar at wavelengths from rest-frame ultraviolet to
rest-frame optical. There are however examples of morphologically selected
spirals and ellipticals at all redshifts up to z ~ 3. At lower redshift, the
bright galaxy population smoothly transforms into normal ellipticals and
spirals. The rate of this transformation strongly depends on redshift, with the
swiftest evolution occurring between 1 < z < 2. This review characterizes the
galaxy structure-redshift relationship, discusses its various physical causes,
and how these are revealing the mechanisms responsible for galaxy formation.Comment: 20 pages, 8 figures. Invited Review to appear in "Penetrating Bars
Through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes A New Note", ed.
D. Block et a
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