411 research outputs found
The portrait of Malin 2: a case study of a giant low surface brightness galaxy
The low surface brightness disc galaxy Malin2 challenges the standard theory
of galaxy evolution by its enormous total mass ~2 10^12 Ms which must have been
formed without recent major merger events. The aim of our work is to create a
coherent picture of this exotic object by using the new optical multicolor
photometric and spectroscopic observations at Apache Point Observatory as well
as archival datasets from Gemini and wide-field surveys. We performed the
Malin2 mass modelling, estimated the contribution of the host dark halo and
found that it had acquired its low central density and the huge isothermal
sphere core radius before the disc subsystem was formed. Our spectroscopic data
analysis reveals complex kinematics of stars and gas in the very inner region.
We measured the oxygen abundance in several clumps and concluded that the gas
metallicity decreases from the solar value in the centre to a half of that at
20-30 kpc. We found a small satellite and measured its mass (1/500 of the host
galaxy) and gas metallicity. One of the unique properties of Malin2 turned to
be the apparent imbalance of ISM: the molecular gas is in excess with respect
to the atomic gas for given values of the gas equilibrium turbulent pressure.
We explain this imbalance by the presence of a significant portion of the dark
gas not observable in CO and the Hi 21 cm lines. We also show that the
depletion time of the observed molecular gas traced by CO is nearly the same as
in normal galaxies. Our modelling of the UV-to-optical spectral energy
distribution favours the exponentially declined SFH over a single-burst
scenario. We argue that the massive and rarefied dark halo which had formed
before the disc component well describes all the observed properties of Malin2
and there is no need to assume additional catastrophic scenarios proposed
previously to explain the origin of giant LSB galaxies. [Abbreviated]Comment: 17 pages, 10 figures, accepted for publication in MNRA
Validation of stellar population and kinematical analysis of galaxies
3D spectroscopy produces hundreds of spectra from which maps of the
characteristics of stellar populations (age-metallicity) and internal
kinematics of galaxies can be derived. We carried on simulations to assess the
reliability of inversion methods and to define the requirements for future
observations. We quantify the biases and show that to minimize the errors on
the kinematics, age and metallicity (in a given observing time) the size of the
spatial elements and the spectral dispersion should be chosen to obtain an
instrumental velocity dispersion comparable to the physical dispersion.Comment: 5 pages, 3 figures, extended version of a poster proceeding to appear
in "Science Perspectives for 3D Spectroscopy", eds. M. Kissler-Patig, M. M.
Roth and J. R. Walsh, ESO Astrophysics Symposia. (The two last pages with
figures are not in the conference proceedings.
Internal Kinematics and Stellar Populations of the Poststarburst+AGN Galaxy SDSS J230743.41+152558.4
We present the first 3D spectroscopic observations of a nearby HI detected
poststarburst, or E+A, galaxy, SDSS J230743.41+152558.4, obtained with the
VIMOS IFU spectrograph at ESO VLT. Using the NBursts full spectral fitting
technique, we derive maps of stellar kinematics, age, and metallicity out to
2-3 half-light radii. Our analysis reveals a large-scale rapidly rotating disc
(v_circ = 300km/s) with a positive age gradient (0.6 to 1.5 Gyr), and a very
metal-rich central region ([Fe/H]=+0.25 dex). If a merger or interaction is
responsible for triggering the starburst, the presence of this undisturbed disc
suggests a minor merger with a gas-rich satellite as the most plausible option,
rather than a disruptive major merger. We find spectroscopic evidence for the
presence of a LINER or AGN. This is an important clue to the feedback mechanism
that truncated the starburst. The presently observed quiescent phase may well
be a temporary episode in the galaxy's life. SDSS J230743.41+152558.4 is
gas-rich and may restart forming stars, again becoming blue before finally
settling at the red sequence.Comment: accepted for publication by Astrophysical Journal Letters, 9 pages, 4
figure
SDSSJ124155.33+114003.7 -- a Missing Link Between Compact Elliptical and Ultracompact Dwarf Galaxies
We report the discovery of a compact object (R_e = 32 pc, M_B = -12.34 mag)
at a projected distance of 9 kpc from Messier 59, a giant elliptical in the
Virgo cluster. Using HST imaging and SDSS spectroscopy, both available in the
Virtual Observatory, we find that this object has a blue core containing
one-quarter of the light, and a redder n=1 Sersic envelope, as well as
luminosity-weighted age of 9.3 +/- 1.4 Gyr, a metallicity of -0.03 +/- 0.04 dex
and a velocity dispersion of 48 +/- 5 km/s. While ultra-compact dwarfs (UCDs)
in the face-on view of the Fundamental Plane are found to form a sequence
connecting the highest-luminosity globular clusters with the lowest-luminosity
dwarf ellipticals, the compact object near M59 lies in between this UCD
sequence and the positions of compact ellipticals. Its stellar age,
metallicity, and effective surface brightness are similar to low-luminosity
ellipticals and lenticulars, suggesting that SDSSJ124155.33+114003.7 is a
result of the tidal stripping of such an object.Comment: 5 pages, 4 figures, accepted to MNRAS Letter
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