11,404 research outputs found
A large narrow band H survey at : the bright end of the luminosity function, cosmic variance and clustering across cosmic time
We carried out the largest ( Mpc, 26 deg) H
narrow band survey to date at in the SA22, W2 and XMMLSS
extragalactic fields. Our survey covers a large enough volume to overcome
cosmic variance and to sample bright and rare H emitters up to an
observed luminosity of erg s, equivalent to yr. Using our sample of sources brighter than
erg s ( yr), we derive H
luminosity functions, which are well described by a Schechter function with
Mpc and
erg s (with a fixed faint end slope ). We find that
surveys probing smaller volumes ( Mpc) are heavily
affected by cosmic variance, which can lead to errors of over per cent in
the characteristic density and luminosity of the H luminosity function.
We derive a star formation rate density of yr, in agreement with the redshift-dependent
H parametrisation from Sobral et al. (2013). The two-point correlation
function is described by a single power law , corresponding to a clustering length of Mpc/h. We find that the most luminous H emitters at
are more strongly clustered than the relatively fainter ones. The
H emitters at in our sample reside in
dark matter haloes. This implies that the most
star forming galaxies always reside in relatively massive haloes or group-like
environments and that the typical host halo mass of star-forming galaxies is
independent of redshift if scaled by , as
proposed by Sobral et al. (2010).Comment: Accepted for publication in MNRAS; 18 pages, 19 figures, 6 table
WHAM Observations of H-Alpha, [S II], and [N II] toward the Orion and Perseus Arms: Probing the Physical Conditions of the Warm Ionized Medium
A large portion of the Galaxy (l = 123 deg to 164 deg, b = -6 deg to -35
deg), which samples regions of the Local (Orion) spiral arm and the more
distant Perseus arm, has been mapped with the Wisconsin H-Alpha Mapper (WHAM)
in the H-Alpha, [S II] 6716, and [N II] 6583 lines. Several trends noticed in
emission-line investigations of diffuse gas in other galaxies are confirmed in
the Milky Way and extended to much fainter emission. We find that the [S
II]/H-Alpha and [N II]/H-Alpha ratios increase as absolute H-Alpha intensities
decrease. For the more distant Perseus arm emission, the increase in these
ratios is a strong function of Galactic latitude and thus, of height above the
Galactic plane. The [S II]/[N II] ratio is relatively independent of H-Alpha
intensity. Scatter in this ratio appears to be physically significant, and maps
of it suggest regions with similar ratios are spatially correlated. The Perseus
arm [S II]/[N II] ratio is systematically lower than Local emission by 10%-20%.
With [S II]/[N II] fairly constant over a large range of H-Alpha intensities,
the increase of [S II]/H-Alpha and [N II]/H-Alpha with |z| seems to reflect an
increase in temperature. Such an interpretation allows us to estimate the
temperature and ionization conditions in our large sample of observations. We
find that WIM temperatures range from 6,000 K to 9,000 K with temperature
increasing from bright to faint H-Alpha emission (low to high [S II]/H-Alpha
and [N II]/H-Alpha) respectively. Changes in [S II]/[N II] appear to reflect
changes in the local ionization conditions (e.g. the S+/S++ ratio). We also
measure the electron scale height in the Perseus arm to be 1.0+/-0.1 kpc,
confirming earlier, less accurate determinations.Comment: 28 pages, 10 figures. Figures 2 and 3 are full color--GIFs provided
here, original PS figures at link below. Accepted for publication in ApJ.
More information about the WHAM project can be found at
http://www.astro.wisc.edu/wham/ . REVISION: Figure 6, bottom panel now
contains the proper points. No other changes have been mad
Integral Field Spectroscopy based H\alpha\ sizes of local Luminous and Ultraluminous Infrared Galaxies. A Direct Comparison with high-z Massive Star Forming Galaxies
Aims. We study the analogy between local U/LIRGs and high-z massive SFGs by
comparing basic H{\alpha} structural characteristics, such as size, and
luminosity (and SFR) surface density, in an homogeneous way (i.e. same tracer
and size definition, similar physical scales). Methods. We use Integral Field
Spectroscopy based H{\alpha} emission maps for a representative sample of 54
local U/LIRGs (66 galaxies). From this initial sample we select 26 objects with
H{\alpha} luminosities (L(H{\alpha})) similar to those of massive (i.e. M\ast
\sim 10^10 M\odot or larger) SFGs at z \sim 2, and observed on similar physical
scales. Results. The sizes of the H{\alpha} emitting region in the sample of
local U/LIRGs span a large range, with r1/2(H{\alpha}) from 0.2 to 7 kpc.
However, about 2/3 of local U/LIRGs with Lir > 10^11.4 L\odot have compact
H{\alpha} emission (i.e. r1/2 < 2 kpc). The comparison sample of local U/LIRGs
also shows a higher fraction (59%) of objects with compact H{\alpha} emission
than the high-z sample (25%). This gives further support to the idea that for
this luminosity range the size of the star forming region is a distinctive
factor between local and distant galaxies of similar SF rates. However, when
using H{\alpha} as a tracer for both local and high-z samples, the differences
are smaller than the ones recently reported using a variety of other tracers.
Despite of the higher fraction of galaxies with compact H{\alpha} emission, a
sizable group (\sim 1/3) of local U/LIRGs are large (i.e. r1/2 > 2 kpc). These
are systems showing pre-coalescence merger activity and they are
indistinguishable from the massive high-z SFGs galaxies in terms of their
H{\alpha} sizes, and luminosity and SFR surface densities.Comment: Accepted for publication in A&A. (!5 pages, 7 figures, 2 tables
On the Origins of the High-Latitude H-alpha Background
The diffuse high-latitude H-alpha background is widely believed to be
predominantly the result of in-situ recombination of ionized hydrogen in the
warm interstellar medium of the Galaxy. Instead, we show that both a
substantial fraction of the diffuse high-latitude H-alpha intensity in regions
dominated by Galactic cirrus dust and much of the variance in the high-latitude
H-alpha background are the result of scattering by interstellar dust of H-alpha
photons originating elsewhere in the Galaxy. We provide an empirical relation,
which relates the expected scattered H-alpha intensity to the IRAS 100um
diffuse background intensity, applicable to about 81% of the entire sky. The
assumption commonly made in reductions of CMB observations, namely that the
observed all-sky map of diffuse H-alpha light is a suitable template for
Galactic free-free foreground emission, is found to be in need of
reexamination.Comment: 26 pages, 5 figures, Accepted for publication in Ap
A complete census of emitters in NGC 6397
We used a dataset of archival Hubble Space Telescope images obtained through
the F555W, F814W and F656N filters, to perform a complete search for objects
showing emission in the globular cluster NGC 6397. As photometric
diagnostic, we used the color excess in the
- color-color diagram. In the analysed field of view,
we identified 53 emitters. In particular, we confirmed the optical
counterpart to 20 X-ray sources (7 cataclysmic variables, 2 millisecond pulsars
and 11 active binaries) and identified 33 previously unknown sources, thus
significantly enlarging the population of known active binaries in this
cluster. We report the main characteristics for each class of objects.
Photometric estimates of the equivalent width of the emission line,
were derived from the -excess and, for the first time, compared
to the spectroscopic measurements obtained from the analysis of MUSE spectra.
The very good agreement between the spectroscopic and photometric measures
fully confirmed the reliability of the proposed approach to measure the
emission. The search demonstrated the efficiency of this novel
approach to pinpoint and measure -emitters, thus offering a powerful
tool to conduct complete census of objects whose formation and evolution can be
strongly affected by dynamical interactions in star clusters.Comment: Accepted for publication by ApJ; 14 pages, 8 Figures, 1 Tabl
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