1,152 research outputs found
Galaxies into the Dark Ages
We consider the capabilities of current and future large facilities operating
at 2\,mm to 3\,mm wavelength to detect and image the [CII] 158\,m line
from galaxies into the cosmic "dark ages" ( to 20). The [CII] line
may prove to be a powerful tool in determining spectroscopic redshifts, and
galaxy dynamics, for the first galaxies. We emphasize that the nature, and even
existence, of such extreme redshift galaxies, remains at the frontier of open
questions in galaxy formation. In 40\,hr, ALMA has the sensitivity to detect
the integrated [CII] line emission from a moderate metallicity, active
star-forming galaxy [; star formation rate (SFR) =
5\,\,yr], at at a significance of 6. The
next-generation Very Large Array (ngVLA) will detect the integrated [CII] line
emission from a Milky-Way like star formation rate galaxy (, SFR = 1\,\,yr), at at a significance
of 6. Imaging simulations show that the ngVLA can determine rotation
dynamics for active star-forming galaxies at , if they exist. Based
on our very limited knowledge of the extreme redshift Universe, we calculate
the count rate in blind, volumetric surveys for [CII] emission at
to 20. The detection rates in blind surveys will be slow (of order unity per
40\,hr pointing). However, the observations are well suited to commensal
searches. We compare [CII] with the [OIII] 88m line, and other ancillary
information in high galaxies that would aid these studies.Comment: 11pages, 8 figures, Accepted for the Astrophysical Journa
Simulating high-redshift galaxies
Recent observations have gathered a considerable sample of high redshift
galaxy candidates and determined the evolution of their luminosity function
(LF). To interpret these findings, we use cosmological SPH simulations
including, in addition to standard physical processes, a detailed treatment of
the Pop III-Pop II transition in early objects. The simulated high-z galaxies
match remarkably well the amplitude and slope of the observed LF in the
redshift range 5<z<10. The LF shifts towards fainter luminosities with
increasing redshift, while its faint-end slope keeps an almost constant value,
\alpha ~-2. The stellar populations of high-z galaxies have ages of 100-300
(40-130) Myr at z=5 (z=7-8), implying an early (z>9.4) start of their star
formation activity; the specific star formation rate is almost independent of
galactic stellar mass. These objects are enriched rapidly with metals and
galaxies identified by HST/WFC3 (M_UV < -18) show metallicities ~0.1 Zsun even
at z=7-8. Most of the simulated galaxies at z~7 (noticeably the smallest ones)
are virtually dust-free, and none of them has an extinction larger than E(B-V)
= 0.01. The bulk (50%) of the ionizing photons is produced by objects
populating the faint-end of the LF (M_UV < -16), which JWST will resolve up to
z=7.3. PopIII stars continue to form essentially at all redshifts; however, at
z=6 (z=10) the contribution of Pop III stars to the total galactic luminosity
is always less than 5% for M_UV < -17 (M_UV < -16). The typical high-z galaxies
closely resemble the GRB host galaxy population observed at lower redshifts,
strongly encouraging the use of GRBs to detect the first galaxies.Comment: 14 pages, 10 figures, MNRAS in pres
Euclid preparation: XXI. Intermediate-redshift contaminants in the search for z>6 galaxies within the Euclid Deep Survey
The author list was incorrect in the published version. The name of the collaboration has been added here
Hubble Space Telescope FUV Spectra of the Post-Common-Envelope Hyades Binary V471 Tauri
We have carried out an analysis of the HST STIS archival spectra of the
magnetic white dwarf in the Hyades eclipsing-spectroscopic, post-common
envelope binary V471 Tauri, time resolved on the orbit and on the X-ray
rotational phase of the magnetic white dwarf. An HST STIS spectrum obtained
during primary eclipse reveals a host of transition region/chromospheric
emission features including N V (1238, 1242), Si IV (1393, 1402), C IV (1548,
1550) and He II (1640). The spectroscopic characteristics and emission line
fluxes of the transition region/chromosphere of the very active, rapidly
rotating, K2V component of V471 Tauri, are compared with the emission
characteristics of fast rotating K dwarfs in young open clusters. We have
detected a number of absorption features associated with metals accreted onto
the photosphere of the magnetic white dwarf from which we derive radial
velocities. All of the absorption features are modulated on the 555s rotation
period of the white dwarf with maximum line strength at rotational phase 0.0
when the primary magnetic accretion region is facing the observer. The
photospheric absorption features show no clear evidence of Zeeman splitting and
no evidence of a correlation between their variations in strength and orbital
phase. We report clear evidence of a secondary accretion pole. We derive C and
Si abundances from the Si IV and C III features. All other absorption lines are
either interstellar or associated with a region above the white dwarf and/or
with coronal mass ejection events illuminated as they pass in front of the
white dwarf.Comment: The Astrophysical Journal, May 10, 2012 issue - 16 figure
- …