220 research outputs found
The Next Generation Space Telescope
In Space Science in the Twenty-First Century, the Space Science Board of the National Research Council identified high-resolution-interferometry and high-throughput instruments as the imperative new initiatives for NASA in astronomy for the two decades spanning 1995 to 2015. In the optical range, the study recommended an 8 to 16-meter space telescope, destined to be the successor of the Hubble Space Telescope (HST), and to complement the ground-based 8 to 10-meter-class telescopes presently under construction. It might seem too early to start planning for a successor to HST. In fact, we are late. The lead time for such major missions is typically 25 years, and HST has been in the making even longer with its inception dating back to the early 1960s. The maturity of space technology and a more substantial technological base may lead to a shorter time scale for the development of the Next Generation Space Telescope (NGST). Optimistically, one could therefore anticipate that NGST be flown as early as 2010. On the other hand, the planned lifetime of HST is 15 years. So, even under the best circumstances, there will be a five year gap between the end of HST and the start of NGST. The purpose of this first workshop dedicated to NGST was to survey its scientific potential and technical challenges. The three-day meeting brought together 130 astronomers and engineers from government, industry and universities. Participants explored the technologies needed for building and operating the observatory, reviewed the current status and future prospects for astronomical instrumentation, and discussed the launch and space support capabilities likely to be available in the next decade. To focus discussion, the invited speakers were asked to base their presentations on two nominal concepts, a 10-meter telescope in space in high earth orbit, and a 16-meter telescope on the moon. The workshop closed with a panel discussion focused mainly on the scientific case, siting, and the programmatic approach needed to bring NGST into being. The essential points of this panel discussion have been incorporated into a series of recommendations that represent the conclusions of the workshop. Speakers were asked to provide manuscripts of their presentation. Those received were reproduced here with only minor editorial changes. The few missing papers have been replaced by the presentation viewgraphs. The discussion that follows each speaker's paper was derived from the question and answer sheets, or if unavailable, from the tapes of the meeting. In the latter case, the editors have made every effort to faithfully represent the discussion
Spectroscopic Confirmation of Multiple Red Galaxy-Galaxy Mergers in MS1054-03 (z=0.83)
We present follow-up spectroscopy of the galaxy cluster MS1054-03 (z=0.83)
confirming that at least six of the nine merging galaxy pairs identified by van
Dokkum et al. (1999) are indeed bound systems: they have projected separations
of R_s<10 kpc and relative line-of sight velocities of dv<165 km/s. For the
remaining three pairs, we were unable to obtain redshifts of both constituent
galaxies. To identify a more objective sample of merging systems, we select
bound red galaxy pairs (R_s<=30 kpc, dv<=300 km/s) from our sample of 121
confirmed cluster members: galaxies in bound red pairs make up 15.7+/-3.6% of
the cluster population. The (B-K_s) color-magnitude diagram shows that the pair
galaxies are as red as the E/S0 members and have a homogeneous stellar
population. The red pair galaxies span a large range in luminosity and internal
velocity dispersion to include some of the brightest, most massive members
(L>L*, sigma>200 km/s); these bound galaxy pairs must evolve into E/S0 members
by z~0.7. These results combined with MS1054's high merger fraction and
reservoir of likely future mergers indicates that most, if not all, of its
early-type members evolved from (passive) galaxy-galaxy mergers at z<~1.Comment: accepted by ApJ Letters; high resolution version of Fig. 2 available
at http://www.exp-astro.phys.ethz.ch/tran/outgoing/ms1054mgrs.ps.g
Ellipticals with Kinematically--Distinct Cores: WFPC2 Imaging of Globular Clusters
Here we present HST WFPC2 imaging of 14 kinematically--distinct core
ellipticals to examine their globular cluster systems. In particular, we probe
the galaxy central regions, for which we might expect to see the strongest
signatures of some formation and destruction processes. These data
substantially increase the number of extragalactic globular cluster systems
studied to date. We find that the globular cluster luminosity, and color, vary
only weakly, if at all, with galactocentric distance. The mean color of
globular clusters are constant with globular cluster magnitude. Several clear
trends are also present. Firstly, globular cluster colors are bluer (more metal
poor by ~ 0.5 dex) than the underlying galaxy starlight at any given
galactocentric distance. Second, we find a correlation over roughly ten
magnitudes between the mean globular cluster metallicity and parent galaxy
luminosity of the form Z goes as L^0.4. This relationship includes dwarf
ellipticals, spiral galaxy bulges and giant ellipticals. Third, we find that
globular cluster surface density distribution can be described by a core model,
for which the core radius correlates with galaxy luminosity. Our results favor
scenarios in which ellipticals form from massive, gas rich progenitors at early
epochs. Detailed simulations of the formation of globular cluster systems would
be valuable to draw firmer conclusions.Comment: text only is given here, 13 figures are available at
http://www.ucolick.org/~forbes/home.html Paper accepted for publication in
the Astrophysical Journa
Optical Spectroscopy of Distant Red Galaxies
We present optical spectroscopic follow-up of a sample of Distant Red
Galaxies (DRGs) with K 2.3, in the Hubble Deep
Field South, the MS 1054-03 field, and the Chandra Deep Field South.
Spectroscopic redshifts were obtained for 15 DRGs. Only 2 out of 15 DRGs are
located at z < 2, suggesting a high efficiency to select high-redshift sources.
From other spectroscopic surveys in the CDFS targeting intermediate to high
redshift populations selected with different criteria, we find spectroscopic
redshifts for a further 30 DRGs. We use the sample of spectroscopically
confirmed DRGs to establish the high quality (scatter in \Delta z/(1+z) of ~
0.05) of their photometric redshifts in the considered deep fields, as derived
with EAZY (Brammer et al. 2008). Combining the spectroscopic and photometric
redshifts, we find that 74% of DRGs with K 2. The combined
spectroscopic and photometric sample is used to analyze the distinct intrinsic
and observed properties of DRGs at z 2. In our photometric sample
to K < 22.5, low-redshift DRGs are brighter in K than high-redshift DRGs by 0.7
mag, and more extincted by 1.2 mag in Av. Our analysis shows that the DRG
criterion selects galaxies with different properties at different redshifts.
Such biases can be largely avoided by selecting galaxies based on their
rest-frame properties, which requires very good multi-band photometry and high
quality photometric redshifts.Comment: Accepted for publication in the Astrophysical Journal, 13 pages, 8
figures, 5 table
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