116 research outputs found
Analysis of the Early-time Optical Spectra of SN 2011fe in M101
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s^(–1)) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^(–1). This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s^(–1). The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta
The DEEP2 Redshift Survey: Lyman Alpha Emitters in the Spectroscopic Database
We present the first results of a search for Lyman-alpha emitters (LAEs) in
the DEEP2 spectroscopic database that uses a search technique that is different
from but complementary to traditional narrowband imaging surveys. We have
visually inspected ~20% of the available DEEP2 spectroscopic data and have
found nine high-quality LAEs with clearly asymmetric line profiles and an
additional ten objects of lower quality, some of which may also be LAEs. Our
survey is most sensitive to LAEs at z=4.4-4.9 and that is indeed where all but
one of our high-quality objects are found. We find the number density of our
spectroscopically-discovered LAEs to be consistent with those found in
narrowband imaging searches. The combined, averaged spectrum of our nine
high-quality objects is well fit by a two-component model, with a second,
lower-amplitude component redshifted by ~420 km/s with respect to the primary
Lyman-alpha line, consistent with large-scale outflows from these objects. We
conclude by discussing the advantages and future prospects of blank-sky
spectroscopic surveys for high-z LAEs.Comment: Accepted for publication in Ap
A Strong-Lens Survey in AEGIS: the influence of large scale structure
We report on the results of a visual search for galaxy-scale strong
gravitational lenses over 650 arcmin^2 of HST/ACS imaging in the DEEP2-EGS
field. In addition to a previously-known Einstein Cross (the "Cross," HST
J141735+52264, with z_lens=0.8106 and a published z_source=3.40), we identify
two new strong galaxy-galaxy lenses with multiple extended arcs. The first, HST
J141820+52361 (the ``Dewdrop''; z_lens=0.5798, lenses two distinct extended
sources into two pairs of arcs z_source=0.while), 9818 the second, HST
J141833+52435 (the ``Anchor''; z_lens=0.4625), produces a single pair of arcs
(source redshift not yet known). All three definite lenses are fit well by
simple singular isothermal ellipsoid models including external shear. Using the
three-dimensional line-of-sight (LOS) information on galaxies from the DEEP2
data, we calculate the convergence and shear contributions, assuming singular
isothermal sphere halos truncated at 200 h^-1 kpc. These are also compared
against three-dimensional local-density estimates. We find that even strong
lenses in demonstrably underdense local environments may be considerably
affected by LOS contributions, which in turn, may be underestimates of the
effect of large scale structure.Comment: ApJ Letters, submitted. Part of the AEGIS ApJL Special Issue. 4
Figures, 1 Table. For a version with full-resolution figures, please see
http://www.slac.stanford.edu/~pjm/HAGGLeS/astroph/legs.pd
Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE
We present initial results of a deep near-IR spectroscopic survey covering
the 15 fields of the Keck Baryonic Structure Survey (KBSS) using MOSFIRE on the
Keck 1 telescope, focusing on a sample of 251 galaxies with redshifts 2.0< z <
2.6, star-formation rates 2 < SFR < 200 M_sun/yr, and stellar masses 8.6 <
log(M*/M_sun) < 11.4, with high-quality spectra in both H- and K-band
atmospheric windows. We show unambiguously that the locus of z~2.3 galaxies in
the "BPT" nebular diagnostic diagram exhibits a disjoint, yet similarly tight,
relationship between the ratios [NII]6585/Halpha and [OIII]/Hbeta as compared
to local galaxies. Using photoionization models, we argue that the offset of
the z~2.3 locus relative to z~ 0 is explained by a combination of harder
ionizing radiation field, higher ionization parameter, and higher N/O at a
given O/H than applies to most local galaxies, and that the position of a
galaxy along the z~2.3 star-forming BPT locus is surprisingly insensitive to
gas-phase oxygen abundance. The observed nebular emission line ratios are most
easily reproduced by models in which the net ionizing radiation field resembles
a blackbody with effective temperature T_eff = 50000-60000 K and N/O close to
the solar value at all O/H. We critically assess the applicability of
commonly-used strong line indices for estimating gas-phase metallicities, and
consider the implications of the small intrinsic scatter in the empirical
relationship between excitation-sensitive line indices and stellar mass (i.e.,
the "mass-metallicity" relation), at z~2.3.Comment: 41 pages, 25 figures, accepted for publication in the Astrophysical
Journal. Version with full-resolution figures available at
http://www.astro.caltech.edu/~ccs/mos_bpt_submit.pd
The DEEP2 Galaxy Redshift Survey: Mean Ages and Metallicities of Red Field Galaxies at z ~ 0.9 from Stacked Keck/DEIMOS Spectra
As part of the DEEP2 galaxy redshift survey, we analyze absorption line
strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no
emission lines, at redshifts 0.7 <= z <= 1. Comparison with models of stellar
population synthesis shows that red galaxies at z ~ 0.9 have mean
luminosity-weighted ages of the order of only 1 Gyr and at least solar
metallicities. This result cannot be reconciled with a scenario where all stars
evolved passively after forming at very high z. Rather, a significant fraction
of stars can be no more than 1 Gyr old, which means that star formation
continued to at least z ~ 1.2. Furthermore, a comparison of these distant
galaxies with a local SDSS sample, using stellar populations synthesis models,
shows that the drop in the equivalent width of Hdelta from z ~ 0.9 to 0.1 is
less than predicted by passively evolving models. This admits of two
interpretations: either each individual galaxy experiences continuing low-level
star formation, or the red-sequence galaxy population from z ~ 0.9 to 0.1 is
continually being added to by new galaxies with younger stars.Comment: A few typos were corrected and numbers in Table 1 were revise
CHIMERA: a wide-field, multi-colour, high-speed photometer at the prime focus of the Hale telescope
The Caltech HIgh-speed Multi-colour camERA (CHIMERA) is a new instrument that has been developed for use at the prime focus of the Hale 200-inch telescope. Simultaneous optical imaging in two bands is enabled by a dichroic beam splitter centred at 567 nm, with Sloan u′ and g′ bands available on the blue arm and Sloan r′, i′ and z_s bands available on the red arm. Additional narrow-band filters will also become available as required. An electron multiplying CCD (EMCCD) detector is employed for both optical channels, each capable of simultaneously delivering sub-electron effective read noise under multiplication gain and frame rates of up to 26 fps full frame (several 1000 fps windowed), over a fully corrected 5 × 5 arcmin field of view. CHIMERA was primarily developed to enable the characterization of the size distribution of sub-km Kuiper Belt Objects via stellar occultation, a science case that motivates the frame-rate, the simultaneous multi-colour imaging and the wide field of view of the instrument. In addition, it also has unique capability in the detection of faint near-Earth asteroids and will be used for the monitoring of short-duration transient and periodic sources, particularly those discovered by the intermediate Palomar Transient Factory (iPTF), and the upcoming Zwicky Transient Facility (ZTF)
Supramolecular assemblies involving metal organic ring interactions: Heterometallic Cu(II)-Ln(III) two dimensional coordination polymers
Three isostructural two-dimensional coordination polymers of the general formula [Ln2(CuL)3(H2O)9]$5.5H2O, where Ln is La (1), Nd (2), and Gd (3), have been synthesized and isolated from aqueous solutions and their single-crystal structures determined by X-ray diffraction. The supramolecular interaction between the non-aromatic metallorings plays an important role in stabilizing the structure of these compounds. The thermal stability, reversible solvent uptake, electronic properties and magnetic studies of these compounds are also reported
The DEEP2 Redshift Survey: Lyα Emitters in the Spectroscopic Database
We present the first results of a search for Lyα emitters (LAEs) in the DEEP2 spectroscopic database that uses a search technique that is different from but complementary to traditional narrowband imaging surveys. We have visually inspected ~20% of the available DEEP2 spectroscopic data and have found nine high-quality LAEs with clearly asymmetric line profiles and an additional 10 objects of lower quality, some of which may also be LAEs. Our survey is most sensitive to LAEs at z = 4.4–4.9 and that is indeed where all but one of our high-quality objects are found. We find the number density of our spectroscopically discovered LAEs to be consistent with those found in narrowband imaging searches. The combined, averaged spectrum of our nine high-quality objects is well fit by a two-component model, with a second, lower amplitude component redshifted by ~420 km s^(−1) with respect to the primary Lyα line, consistent with large-scale outflows from these objects. We conclude by discussing the advantages and future prospects of blank-sky spectroscopic surveys for high-z LAEs
Galaxy Luminosity Functions to z~1: DEEP2 vs. COMBO-17 and Implications for Red Galaxy Formation
The DEEP2 and COMBO-17 surveys are used to study the evolution of the
luminosity function of red and blue galaxies to . Schechter function
fits show that, since , dims by 1.3 mag per unit redshift
for both color classes, of blue galaxies shows little change, while
for red galaxies has formally nearly quadrupled. At face value, the
number density of blue galaxies has remained roughly constant since ,
whereas that of red galaxies has been rising. Luminosity densities support both
conclusions, but we note that most red-galaxy evolution occurs between our data
and local surveys and in our highest redshift bin, where the data are weakest.
We discuss the implications of having most red galaxies emerge after
from precursors among the blue population, taking into account the properties
of local and distant E/S0s. We suggest a ``mixed'' scenario in which some blue
galaxies have their star-formation quenched in gas-rich mergers, migrate to the
red sequence with a variety of masses, and merge further on the red sequence in
one or more purely stellar mergers. E/S0s of a given mass today will have
formed via different routes, in a manner that may help to explain the
fundamental plane and other local scaling laws.Comment: Submitted to ApJ. 73 pages, 12 figures. Part II of a two-paper
series. The entire paper is available as a single postscript file at:
http://www.ucolick.org/~cnaw/paper2_submitted.ps.g
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