69 research outputs found
The 300km/s stellar stream near Segue 1: Insights From high-resolution spectroscopy of its brightest star
We present a chemical abundance analysis of 300S-1, the brightest likely
member star of the 300 km/s stream near the faint satellite galaxy Segue 1.
From a high-resolution Magellan/MIKE spectrum we determine a metallicity of
[Fe/H] = -1.46 +- 0.05 +- 0.23 (random and systematic uncertainties) for star
300S-1, and find an abundance pattern similar to typical halo stars at this
metallicity. Comparing our stellar parameters to theoretical isochrones, we
estimate a distance of 18 +- 7 kpc. Both the metallicity and distance estimates
are in good agreement with what can be inferred from comparing the SDSS
photometric data of the stream stars to globular cluster sequences. While
several other structures overlap with the stream in this part of the sky, the
combination of kinematic, chemical and distance information makes it unlikely
that these stars are associated with either the Segue 1 galaxy, the Sagittarius
stream or the Orphan stream. Streams with halo-like abundance signatures, such
as the 300 km/s stream, present another observational piece for understanding
the accretion history of the Galactic halo.Comment: 13 pages, emulateapj, accepted for publication in Ap
The 300 km s -1 stellar stream near Segue 1: Insights from high-resolution spectroscopy of its brightest star
We present a chemical abundance analysis of 300S-1, the brightest likely member star of the 300 km s-1 stream near the faint satellite galaxy Segue 1. From a high-resolution Magellan/MIKE spectrum, we determine a metallicity of [Fe/H] = -1.46 ± 0.05 ±
The Intermediate Luminosity Optical Transient SN 2010da: The Progenitor, Eruption and Aftermath of a Peculiar Supergiant High-mass X-ray Binary
We present optical spectroscopy, ultraviolet to infrared imaging and X-ray
observations of the intermediate luminosity optical transient (ILOT) SN 2010da
in NGC 300 (d=1.86 Mpc) spanning from -6 to +6 years relative to the time of
outburst in 2010. Based on the light curve and multi-epoch SEDs of SN 2010da,
we conclude that the progenitor of SN 2010da is a ~10-12 Msol yellow supergiant
possibly transitioning into a blue loop phase. During outburst, SN 2010da had a
peak absolute magnitude of M<-10.4 mag, dimmer than other ILOTs and supernova
impostors. We detect multi-component hydrogen Balmer, Paschen, and Ca II
emission lines in our high-resolution spectra, which indicate a dusty and
complex circumstellar environment. Since the 2010 eruption, the star has
brightened by a factor of ~5 and remains highly variable in the optical.
Furthermore, we detect SN 2010da in archival Swift and Chandra observations as
an ultraluminous X-ray source (L~6x10^{39} erg/s). We additionally attribute He
II 4686 Angstrom and coronal Fe emission lines in addition to a steady X-ray
luminosity of ~10^{37} erg/s to the presence of a compact companion.Comment: published; updated citations and other minor edit
Short GRB 130603B: Discovery of a jet break in the optical and radio afterglows, and a mysterious late-time X-ray excess
We present radio, optical/NIR, and X-ray observations of the afterglow of the
short-duration 130603B, and uncover a break in the radio and optical bands at
0.5 d after the burst, best explained as a jet break with an inferred jet
opening angle of 4-8 deg. GRB 130603B is only the third short GRB with a radio
afterglow detection to date, and the first time that a jet break is evident in
the radio band. We model the temporal evolution of the spectral energy
distribution to determine the burst explosion properties and find an
isotropic-equivalent kinetic energy of (0.6-1.7) x 10^51 erg and a circumburst
density of 5 x 10^-3-30 cm^-3. From the inferred opening angle of GRB 130603B,
we calculate beaming-corrected energies of Egamma (0.5-2) x 10^49 erg and EK
(0.1-1.6) x 10^49 erg. Along with previous measurements and lower limits we
find a median short GRB opening angle of 10 deg. Using the all-sky observed
rate of 10 Gpc^-3 yr^-1, this implies a true short GRB rate of 20 yr^-1 within
200 Mpc, the Advanced LIGO/VIRGO sensitivity range for neutron star binary
mergers. Finally, we uncover evidence for significant excess emission in the
X-ray afterglow of GRB 130603B at >1 d and conclude that the additional energy
component could be due to fall-back accretion or spin-down energy from a
magnetar formed following the merger.Comment: Submitted to ApJ; emulateapj style; 10 pages, 1 table, 3 figure
Using the Topology of Large Scale Structure to constrain Dark Energy
The use of standard rulers, such as the scale of the Baryonic Acoustic
oscillations (BAO), has become one of the more powerful techniques employed in
cosmology to probe the entity driving the accelerating expansion of the
Universe. In this paper, the topology of large scale structure (LSS) is used as
one such standard ruler to study this mysterious `dark energy'. By following
the redshift evolution of the clustering of luminous red galaxies (LRGs) as
measured by their 3D topology (counting structures in the cosmic web), we can
chart the expansion rate and extract information about the equation of state of
dark energy. Using the technique first introduced in (Park & Kim, 2009), we
evaluate the constraints that can be achieved using 3D topology measurements
from next-generation LSS surveys such as the Baryonic Oscillation Spectroscopic
Survey (BOSS). In conjunction with the information that will be available from
the Planck satellite, we find a single topology measurement on 3 different
scales is capable of constraining a single dark energy parameter to within 5%
and 10% when dynamics are permitted. This offers an alternative use of the data
available from redshift surveys and serves as a cross-check for BAO studies.Comment: 8 pages, 5 figures, 2 tables, Submitted to MNRAS, updated
acknowledgement
On the Populations of Radio Galaxies with Extended Morphology at z<0.3
Extended extragalactic radio sources have traditionally been classified into
FR I and II types, based on the ratio r of the separation S between the
brightest regions on either sides of the host galaxy and the total size T of
the radio source. Here we examine the distribution of various physical
properties as a function of r of 1040 luminous radio galaxies (RGs) at z<0.3
from the SDSS, NVSS, and FIRST. About 2/3 of the RGs are lobe-dominated (LD),
and 1/3 have prominent jets. If we follow the original definition of the FR
types (a division based solely on r), FR I and FR II RGs overlap in their host
galaxy properties. However, the rare, LD sources with r>0.8 AND OIII5007 line
luminosity >10^6 Lsun are markedly different on average from the rest of the
RGs, in the sense that they are hosted in lower mass galaxies, live in
relatively sparse environments, and have higher accretion rates onto the
central SMBH. Thus these objects and the rest of RGs form a well-defined
dichotomy. Motivated by the stark differences in the nuclear emission line
properties of the RG subsamples, we suggest that the accretion rate onto the
SMBH may play the primary role in creating the different morphologies. At
relatively high accretion rates, the accretion system may produce powerful jets
that create the "classical double" morphology (roughly corresponding to the LD
sources with r>0.8 and emission lines); at lower accretion rates the jets from
a radiatively inefficient accretion flow generate radio lobes without apparent
"hot spots" at the edge (corresponding to the majority of LD sources). At
slightly lower accretion rates AND in galaxies with dense galactic structure,
sources with prominent jets result. It is possible that while the high
accretion rate systems could affect sub-Mpc scale environments, the jets from
lower accretion rate systems may efficiently suppress activity within the host
galaxies.Comment: ApJ, accepted. 20 pages, 16 figures, 4 tables. Image quality of
Figures 1 & 2 degraded due to size limits. Table 4 is available and kept
up-to-date at http://member.ipmu.jp/yen-ting.lin/RG/index.html. Higher
resolution version available at
http://member.ipmu.jp/yen-ting.lin/Data/ytlin.pd
Recommended from our members
GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar Medium in a Star-forming Galaxy in the First Gyr After the Big Bang
We present high signal-to-noise ratio Gemini and MMT spectroscopy of the optical afterglow of the gamma-ray burst (GRB) 130606A at redshift z=5.913, discovered by Swift. This is the first high-redshift GRB afterglow to have spectra of comparable quality to those of z ≈ 6 quasars. The data exhibit a smooth continuum at near-infrared wavelengths that is sharply cut off blueward of 8410 ˚A due to absorption from Lyα at redshift z ≈ 5.91, with some flux transmitted through the Lyα forest between 7000−7800 ˚A. We use column densities inferred from metal absorption lines to constrain the metallicity of the host galaxy between a lower limit of [Si/H]&−1.7 and an upper limit of [S/H].−0.5 set by the non-detection of S II absorption. We demonstrate consistency between the dramatic evolution in the transmission fraction of Lyα seen in this spectrum over the redshift range z = 4.9 to 5.85 with that previously measured from observations of high-redshift quasars. There is an extended redshift interval of ∆z=0.12 in the Lyα forest at z=5.77 with no detected transmission, leading to a 3σ upper limit on the mean Lyα transmission fraction of .0.2% (or τ eff GP(Lyα)>6.4). This is comparable to the lowest-redshift Gunn-Peterson troughs found in quasar spectra. Some Lyβ and Lyγ transmission is detected in this redshift window, indicating that it is not completely opaque, and hence that the IGM is nonetheless mostly ionized at these redshifts. We set a 2σ upper limit of 0.11 on the neutral fraction of the IGM at the redshift of the GRB from the lack of a Lyα red damping wing, assuming a model with a constant neutral density. GRB 130606A thus for the first time realizes the promise of GRBs as probes of the first galaxies and cosmic reionization.Astronom
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