1,491 research outputs found
Properties of the Molecular Cores of Low Luminosity Objects
We present a survey toward 16 Low Luminosity Objects (LLOs with an internal
luminosity, Lint, lower than 0.2 Lsun) with N2H+ (1-0), N2H+ (3-2), N2D+ (3-2),
HCO+ (3-2) and HCN (3-2) using the Arizona Radio Observatory Kitt Peak 12m
Telescope and Submillimeter Telescope. Our goal is to probe the nature of these
faint protostars which are believed to be either very low mass or extremely
young protostars. We find that the N2D+/N2H+ column density ratios of LLOs are
similar to those of typical starless cores and Class 0 objects. The N2D+/N2H+
column density ratios are relatively high (> 0.05) for LLOs with kinetic
temperatures less than 10 K in our sample. The distribution of N2H+ (1-0) line
widths spreads between that of starless cores and young Class 0 objects. If we
use the line width as a dynamic evolutionary indicator, LLOs are likely young
Class 0 protostellar sources. We further use the optically thick tracers, HCO+
(3-2) and HCN (3-2), to probe the infall signatures of our targets. We derive
the asymmetry parameters from both lines and estimate the infall velocities by
fitting the HCO+ (3-2) spectra with two-layer models. As a result, we identify
eight infall candidates based on the infall velocities and seven candidates
have infall signatures supported by asymmetry parameters from at least one of
HCO+ (3-2) and HCN (3-2).Comment: 15 pages, 8 figures, accepted to Ap
The Evolution of Density Structure of Starless and Protostellar Cores
We present a near-infrared extinction study of nine dense cores at
evolutionary stages between starless to Class I. Our results show that the
density structure of all but one observed cores can be modeled with a single
power law rho \propto r^p between ~ 0.2R-R of the cores. The starless cores in
our sample show two different types of density structures, one follows p ~ -1.0
and the other follows p ~ -2.5, while the protostellar cores all have p ~ -2.5.
The similarity between the prestellar cores with p ~ -2.5 and protostellar
cores implies that those prestellar cores could be evolving towards the
protostellar stage. The slope of p ~ -2.5 is steeper than that of an singular
isothermal sphere, which may be interpreted with the evolutionary model of
cores with finite mass.Comment: 19 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Recommended from our members
Lysophosphatidic Acid and Hematopoiesis: From Microenvironmental Effects to Intracellular Signaling.
Vertebrate hematopoiesis is a complex physiological process that is tightly regulated by intracellular signaling and extracellular microenvironment. In recent decades, breakthroughs in lineage-tracing technologies and lipidomics have revealed the existence of numerous lipid molecules in hematopoietic microenvironment. Lysophosphatidic acid (LPA), a bioactive phospholipid molecule, is one of the identified lipids that participates in hematopoiesis. LPA exhibits various physiological functions through activation of G-protein-coupled receptors. The functions of these LPARs have been widely studied in stem cells, while the roles of LPARs in hematopoietic stem cells have rarely been examined. Nonetheless, mounting evidence supports the importance of the LPA-LPAR axis in hematopoiesis. In this article, we have reviewed regulation of hematopoiesis in general and focused on the microenvironmental and intracellular effects of the LPA in hematopoiesis. Discoveries in these areas may be beneficial to our understanding of blood-related disorders, especially in the context of prevention and therapy for anemia
Kinematic classifications of local interacting galaxies: implications for the merger/disk classifications at high-z
The classification of galaxy mergers and isolated disks is key for
understanding the relative importance of galaxy interactions and secular
evolution during the assembly of galaxies. The kinematic properties of galaxies
as traced by emission lines have been used to suggest the existence of a
significant population of high-z star-forming galaxies consistent with isolated
rotating disks. However, recent studies have cautioned that post-coalescence
mergers may also display disk-like kinematics. To further investigate the
robustness of merger/disk classifications based on kinematic properties, we
carry out a systematic classification of 24 local (U)LIRGs spanning a range of
galaxy morphologies: from isolated spiral galaxies, ongoing interacting
systems, to fully merged remnants. We artificially redshift the WiFeS
observations of these local (U)LIRGs to z=1.5 to make a realistic comparison
with observations at high-z, and also to ensure that all galaxies have the same
spatial sampling of ~900 pc. Using both kinemetry-based and visual
classifications, we find that the reliability of kinematic classification shows
a strong trend with the interaction stage of galaxies. Mergers with two nuclei
and tidal tails have the most distinct kinematic properties compared to
isolated disks, whereas a significant population of the interacting disks and
merger remnants are indistinguishable from isolated disks. The high fraction of
late-stage mergers showing disk-like kinematics reflects the complexity of the
dynamics during galaxy interactions. However, the exact fractions of
misidentified disks and mergers depend on the definition of kinematic
asymmetries and the classification threshold when using kinemetry-based
classifications. Our results suggest that additional indicators such as
morphologies traced by stars or molecular gas are required to further constrain
the merger/disk classifications at high-z.Comment: 16 pages, 5 figures, ApJ accepte
Variations of the ISM Compactness Across the Main Sequence of Star-Forming Galaxies: Observations and Simulations
(abridged) The majority of star-forming galaxies follow a simple empirical
correlation in the star formation rate (SFR) versus stellar mass () plane,
usually referred to as the star formation Main Sequence (MS). Here we combine a
set of hydro-dynamical simulations of interacting galactic disks with
state-of-the-art radiative transfer codes to analyze how the evolution of
mergers is reflected upon the properties of the MS. We present
\textsc{Chiburst}, a Markov Chain Monte Carlo (MCMC) Spectral Energy
Distribution (SED) code that fits the multi-wavelength, broad-band photometry
of galaxies and derives stellar masses, star formation rates, and geometrical
properties of the dust distribution. We apply this tool to the SEDs of
simulated mergers and compare the derived results with the reference output
from the simulations. Our results indicate that changes in the SEDs of mergers
as they approach coalescence and depart from the MS are related to an evolution
of dust geometry in scales larger than a few hundred parsecs. This is reflected
in a correlation between the specific star formation rate (sSFR), and the
compactness parameter , that parametrizes this geometry and hence
the evolution of dust temperature () with time. As mergers
approach coalescence, they depart from the MS and increase their compactness,
which implies that moderate outliers of the MS are consistent with late-type
mergers. By further applying our method to real observations of Luminous
Infrared Galaxies (LIRGs), we show that the merger scenario is unable to
explain these extreme outliers of the MS. Only by significantly increasing the
gas fraction in the simulations are we able to reproduce the SEDs of LIRGs.Comment: 18 pages, 10 figures, accepted in Ap
Galaxy Alignments in Very X-ray Luminous Clusters at z>0.5
We present the results of a search for galaxy alignments in 12 galaxy
clusters at z>0.5, a statistically complete subset of the very X-ray luminous
clusters from the MAssive Cluster Survey (MACS). Using high-quality images
taken with the Hubble Space Telescope (HST) that render measurement errors
negligible, we find no radial galaxy alignments within 500 kpc of the cluster
centres for a sample of 545 spectroscopically confirmed cluster members. A
mild, but statistically insignificant trend favouring radial alignments is
observed within a radius of 200 kpc and traced to galaxies on the cluster red
sequence. Our results for massive clusters at z>0.5 are in stark contrast to
the findings of previous studies which find highly significant radial
alignments of galaxies in nearby clusters at z~0.1 out to at least half the
virial radius using imaging data from the SDSS. The discrepancy becomes even
more startling if radial alignment becomes more prevalent at decreasing
clustercentric distance, as suggested by both our and previous work. We
investigate and discuss potential causes for the disparity between our findings
based on HST images of clusters at z>0.5 and those obtained using groundbased
images of systems at z~0.1. We conclude that the most likely explanation is
either dramatic evolution with redshift (in the sense that radial alignments
are less pronounced in dynamically younger systems) or the presence of
systematic biases in the analysis of SDSS imaging data that cause at least
partly spurious alignment signals.Comment: 10 pages, 11 figures, and 1 table. Accepted for publication in MNRA
Orthogonal Tip-to-Tip Nanocapillary Alignment Allows for Easy Detection of Fluorescent Emitters in Femtomolar Concentrations
Here we present the realization of a novel fluorescence detection method based on the electromigration of fluorescent molecules within a nanocapillary combined with the laser excitation through a platinum (Pt)-coated nanocapillary. By using the Pt nanocapillary assisted focusing of a laser beam, we completely remove the background scattering on the tip of the electrophoretic nanocapillary. In this excitation geometry, we demonstrate a 1000-fold sensitivity enhancement (1.0 nM to 1.0 pM) compared to the detection in microcapillaries with epifluorescence illumination and fluorescence spectrophotometry. Due to a significant electroosmotic flow, we observe a decelerating migration of DNA molecules close to the tip of the electrophoretic nanocapillary. The reduced DNA translocation velocity causes a two-step stacking process of molecules in the tip of the nanocapillary and can be used as a way to locally concentrate molecules. The sensitivity of our method is further improved by a continuous electrokinetic injection of DNA molecules followed by sample zone stacking on the tip of the nanocapillary. Concentrations ranging from 0.1 pM to 1.0 fM can be directly observed on the orifice of the electrophoretic nanocapillary. This is a 1000-fold improvement compared to traditional capillary electrophoresis with laser-induced fluorescence
SDSS1133: An Unusually Persistent Transient in a Nearby Dwarf Galaxy
While performing a survey to detect recoiling supermassive black holes, we
have identified an unusual source having a projected offset of 800 pc from a
nearby dwarf galaxy. The object, SDSS J113323.97+550415.8, exhibits broad
emission lines and strong variability. While originally classified as a
supernova (SN) because of its nondetection in 2005, we detect it in recent and
past observations over 63 yr and find over a magnitude of rebrightening in the
last 2 years. Using high-resolution adaptive optics observations, we constrain
the source emission region to be <12 pc and find a disturbed host-galaxy
morphology indicative of recent merger activity. Observations taken over more
than a decade show narrow [O III] lines, constant ultraviolet emission, broad
Balmer lines, a constant putative black hole mass over a decade of observations
despite changes in the continuum, and optical emission-line diagnostics
consistent with an active galactic nucleus (AGN). However, the optical spectra
exhibit blueshifted absorption, and eventually narrow Fe II and [Ca II]
emission, each of which is rarely found in AGN spectra. While this peculiar
source displays many of the observational properties expected of a potential
black hole recoil candidate, some of the properties could also be explained by
a luminous blue variable star (LBV) erupting for decades since 1950, followed
by a Type IIn SN in 2001. Interpreted as an LBV followed by a SN analogous to
SN 2009ip, the multi-decade LBV eruptions would be the longest ever observed,
and the broad Halpha emission would be the most luminous ever observed at late
times (>10 yr), larger than that of unusually luminous supernovae such as SN
1988Z, suggesting one of the most extreme episodes of pre-SN mass loss ever
discovered.Comment: Accepted for publication in MNRA
- …