104 research outputs found
Oxygen Gas Abundances at 0.4<z<1.5: Implications for the Chemical Evolution History of Galaxies
We report VLT-ISAAC and Keck-NIRSPEC near-infrared spectroscopy for a sample
of 30 0.47<z<0.92 CFRS galaxies and five [OII]-selected, M_B,AB<-21.5, z~1.4
galaxies. We have measured Halpha and [NII] line fluxes for the CFRS galaxies
which have [OII], Hbeta and [OIII] line fluxes available from optical
spectroscopy. For the z~1.4 objects we measured Hbeta and [OIII] emission line
fluxes from J-band spectra, and Halpha line fluxes plus upper limits for [NII]
fluxes from H-band spectra. We derive the extinction and oxygen abundances for
the sample using a method based on a set of ionisation parameter and oxygen
abundance diagnostics, simultaneously fitting the [OII], Hbeta, [OIII], Halpha
and [NII] line fluxes. Our most salient conclusions are: a) the source of gas
ionisation in the 30 CFRS and in all z~1.4 galaxies is not due to AGN activity;
b) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have
substantially lower metallicities than local galaxies with similar luminosities
and star formation rates; c) comparison with a chemical evolution model
indicates that these low metallicity galaxies are unlikely to be the
progenitors of metal-poor dwarf galaxies at z~0, but more likely the
progenitors of massive spirals; d) the z~1.4 galaxies are characterized by the
high [OIII]/[OII] line ratios, low extinction and low metallicity that are
typical of lower luminosity CADIS galaxies at 0.4<z<0.7, and of more luminous
Lyman Break Galaxies at z~3.1, but not seen in CFRS galaxies at 0.4<z<1.0; e)
the properties of the z~1.4 galaxies suggest that the period of rapid chemical
evolution takes place progressively in lower mass systems as the universe ages,
and thus provides further support for a downsizing picture of galaxy formation,
at least from z~1.4 to today.Comment: Proceedings contribution for "The Fabulous Destiny of Galaxies;
Bridging Past and Present", Marseille, 200
Progressive Star Bursts and High Velocities in the Infrared Luminous, Colliding Galaxy Arp 118
In this paper we demonstrate for the first time the connection between the
spatial and temporal progression of star formation and the changing locations
of the very dense regions in the gas of a massive disk galaxy (NGC 1144) in the
aftermath of its collision with a massive elliptical (NGC 1143). These two
galaxies form the combined object Arp 118, a collisional ring galaxy system.
The results of 3D, time-dependent, numerical simulations of the behavior of the
gas, stars, and dark matter of a disk galaxy and the stars and dark matter in
an elliptical during a collision are compared with multiwavelength observations
of Arp 118. The collision that took place approximately 22 Myr ago generated a
strong, non-linear density wave in the stars and gas in the disk of NGC 1144,
causing the gas to became clumped on a large scale. This wave produced a series
of superstarclusters along arcs and rings that emanate from the central point
of impact in the disk. The locations of these star forming regions match those
of the regions of increased gas density predicted the time sequence of models.
The models also predict the large velocity gradients observed across the disk
of NGC 1144. These are due to the rapid radial outflow of gas coupled to large
azimuthal velocities in the expanding ring, caused by the impact of the massive
intruder.Comment: 12 pages in document, and 8 figures (figures are separate from the
document's file); Submitted to Astrophysical Journal Letter
Distant galaxy clusters in the COSMOS field found by HIROCS
We present the first high-redshift galaxy cluster candidate sample from the
HIROCS survey found in the COSMOS field. It results from a combination of
public COSMOS with proprietary H-band data on a 0.66 square degree part of the
COSMOS field and comprises 12 candidates in the redshift range 1.23 < z < 1.55.
We find an increasing fraction of blue cluster members with increasing
redshift. Many of the blue and even some of the reddest member galaxies exhibit
disturbed morphologies as well as signs of interaction.Comment: 5 pages, 5 figures, in print format, accepted for publication by A&A
Letter
The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics
We present observations of the distribution and kinematics of neutral and
ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system.
Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk
of NGC 1144, but HI emission is detected over only 1/3 of this velocity range,
in an area that corresponds to the NW half of the disk. In the nuclear region
of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is
observed. Faint, narrow HI absorption lines are also detected against radio
sources in the SE part of the disk of NGC 1144, which includes regions of
massive star formation and a Seyfert nucleus. The peculiar HI distribution,
which is concentrated in the NW disk, seems to be the inverse of the molecular
distribution which is concentrated in the SE disk. Although this may partly be
the result of the destruction of HI clouds in the SE disk, there is
circumstantial evidence that the entire HI emission spectrum of NGC 1144 is
affected by a deep nuclear absorption line covering a range of 600 km/s, and is
likely blueshifted with respect to the nucleus. In this picture, a high
column-density HI stream is associated with the nuclear ionized gas velocity
discontinuity, and the absorption effectively masks any HI emission that would
be present in the SE disk of NGC 1144.Comment: manuscript, arp118.ps: 28 pages; 1 Table: arp118.tab1.ps; 16 Figures:
arp118.fig1-16.ps; Accepted to Ap
The metallicity-luminosity relation at medium redshift based on faint CADIS emission line galaxies
The emission line survey within the Calar Alto Deep Imaging Survey (CADIS)
detects galaxies with very low continuum brightness by using an imaging
Fabry-Perot interferometer. With spectroscopic follow-up observations of
MB>~-19 CADIS galaxies using FORS2 at the VLT and DOLORES at TNG we obtained
oxygen abundances of 5 galaxies at z~0.4 and 10 galaxies at z~0.64. Combining
these measurements with published oxygen abundances of galaxies with MB<~-19 we
find evidence that a metallicity-luminosity relation exists at medium redshift,
but it is displaced to lower abundances and higher luminosities compared to the
metallicity-luminosity relation in the local universe. Comparing the observed
metallicities and luminosities of galaxies at z<3 with Pegase2 chemical
evolution models we have found a favoured scenario in which the metallicity of
galaxies increases by a factor of ~2 between z~0.7 and today, and their
luminosity decreases by ~0.5-0.9mag.Comment: Accepted for publication in A&A; 12 pages, 9 figure
Oxygen Gas Abundances at z~1.4: Implications for the Chemical Evolution History of Galaxies
The 1<z<2 redshift window hosts the peak of the star formation and metal
production rates. Studies of the metal content of the star forming galaxies at
these epochs are however sparse. We report VLT-ISAAC near-infrared spectroscopy
for a sample of five [OII]-selected, M_B,AB<-21.5, z~1.4 galaxies, by which we
measured Hbeta and [OIII]5007 emission line fluxes from J-band spectra, and
Halpha line fluxes plus upper limits for [NII]6584 fluxes from H-band spectra.
The z~1.4 galaxies are characterized by the high [OIII]/[OII] line ratios, low
extinction and low metallicity that are typical of lower luminosity CADIS
galaxies at 0.4<z<0.7, and of more luminous Lyman Break Galaxies at z~3, but
not seen in CFRS galaxies at 0.4<z<0.9. This type of spectrum (e.g., high
[OIII]/[OII]) is seen in progressively more luminous galaxies as the redshift
increases. These spectra are caused by a combination of high ionisation
parameter q and lower [O/H]. Pegase2 chemical evolution models are used to
relate the observed metallicities and luminosities of z~1.4 galaxies to galaxy
samples at lower and higher redshift. Not surpringsingly, we see a relationship
between redshift and inferred chemical age. We suppose that the metal-enriched
reservoirs of star forming gas that we are probing at intermediate redshifts
are being mostly consumed to build up both the disk and the bulge components of
spiral galaxies. Finally, our analysis of the metallicity-luminosity relation
at 0<z<1.5 suggests that the period of rapid chemical evolution may take place
progressively in lower mass systems as the universe ages. These results are
consistent with a ``downsizing'' type picture in the sense that particular
signatures (e.g., high [OIII]/[OII] or low [O/H]) are seen in progressively
more luminous (massive) systems at higher redshifts.Comment: Accepted for publication in Ap
Molecular Gas in the Spectacular Ring Galaxy NGC 1144
We have detected extremely wide (1100 km/s) CO(1-0) emission from NGC 1144,
an interacting, luminous infrared galaxy that is the dominant component of the
Arp 118 system. The observations show that NGC 1144 is one of the most CO
luminous galaxies in the local universe, with a CO luminosity twice that of Arp
220. Maps with the IRAM interferometer show that the CO is not in or very near
the Seyfert 2 nucleus, but in the 20 kpc diameter ring that extends halfway
between NGC 1144 and the elliptical galaxy NGC 1143. The greatest gas
concentration, with 40% of the CO luminosity, is in the southern part of the
ring, in NGC 1144. Another 15% of the CO luminosity comes from the dominant 10
m source, a giant extranuclear HII region. The ring of molecular gas, the
off-center nucleus, the ring extending halfway to the intruder, and the
velocity of the intruder nearly equal to the escape velocity all show that Arp
118 is a ring galaxy produced by a collision of a massive spiral with an
elliptical. The most spectacular property is the velocity range, which in Arp
118 is 2 to 3 times higher than in a typical ring galaxy. Arp 118 is a rare
example of a very luminous extended starburst with a scale of about 5-10 kpc,
and a luminosity of 3 .Comment: AAS Latex with postscript figures. Note that two negative signs ("-")
in Declination were missed from Fig. 2. ApJ Letters (in press
The Luminosity Function Of Field Galaxies And Its Evolution Since z=1
We present the B-band luminosity function and comoving space and luminosity
densities for a sample of 2779 I-band selected field galaxies based on
multi-color data from the CADIS survey. The sample is complete down to I_815 =
22 without correction and with completeness correction extends to I_815=23.0.
By means of a new multi-color analysis the objects are classified according to
their spectral energy distributions (SEDs) and their redshifts are determined
with typical errors of delta z <= 0.03. We have split our sample into four
redshift bins between z=0.1 and z=1.04 and into three SED bins E-Sa,Sa-Sc and
starbursting (emission line) galaxies. The evolution of the luminosity function
is clearly differential with SED. The normalization phi* of luminosity function
for the E-Sa galaxies decreases towards higher redshift, and we find evidence
that the comoving galaxy space density decreases with redshift as well. In
contrast, we find phi* and the comoving space density increasing with redshift
for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the
luminosity function at the faint end and their comoving space density increases
with redshift.Comment: 15 pages, 14 figures, accepted by Astronomy&Astrophysic
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