Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe LAMOST Survey of Background Quasars in the Vicinity of the Andromeda and Triangulum Galaxies -- II. Results from the Commissioning Observations and the Pilot Surveys
91
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present new quasars discovered in the vicinity of the Andromeda and Triangulum galaxies with the LAMOST during the 2010 and 2011 observational seasons. Quasar candidates are selected based on the available SDSS, KPNO 4 m telescope, XSTPS optical, and WISE near infrared photometric data. We present 509 new quasars discovered in a stripe of ~135 sq. deg from M31 to M33 along the Giant Stellar Stream in the 2011 pilot survey datasets, and also 17 new quasars discovered in an area of ~100 sq. deg that covers the central region and the southeastern halo of M31 in the 2010 commissioning datasets. These 526 new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to 3.2. They represent a significant increase of the number of identified quasars in the vicinity of M31 and M33. There are now 26, 62 and 139 known quasars in this region of the sky with i magnitudes brighter than 17.0, 17.5 and 18.0 respectively, of which 5, 20 and 75 are newly-discovered. These bright quasars provide an invaluable collection with which to probe the kinematics and chemistry of the ISM/IGM in the Local Group of galaxies. A total of 93 quasars are now known with locations within 2.5 deg of M31, of which 73 are newly discovered. Tens of quasars are now known to be located behind the Giant Stellar Stream, and hundreds behind the extended halo and its associated substructures of M31. The much enlarged sample of known quasars in the vicinity of M31 and M33 can potentially be utilized to construct a perfect astrometric reference frame to measure the minute PMs of M31 and M33, along with the PMs of substructures associated with the Local Group of galaxies. Those PMs are some of the most fundamental properties of the Local Group.
rate research
Read More
Quasars and active galactic nuclei (AGN) are significant contributors to the metagalactic ionizing background at redshifts z < 3. Recent HST/COS composite spectra of AGN find a harder flux distribution in the Lyman continuum, F_nu ~ nu^{-alpha_s} (alpha_s = 1.41+/-0.15) compared to previous studies. This index appears to be inconsistent with observed He II / H I absorption ratios (eta) in the Lya forest. We explore effects of internal AGN absorption in the He II (4 ryd) continuum using an analytic source-function model of the ionizing background in which the emissivity (j_nu) arises from quasars, reprocessed by the opacity (kappa_nu) of the intervening Lya forest and distinct AGN escape fractions f_esc(HI) and f_esc(HeII) at 1~ryd and 4~ryd, respectively. We also examine H I and He II photoelectric heating from the reprocessed background, whose spectral index (alpha_b > alpha_s) depends on alpha_s, the H I column density slope beta, and the ratio R = f_esc(HI) / f_esc(HeII). We compare the model to Lya absorption lines of He II and H I toward the quasar HE~2347-4342. Internal AGN absorption with f_esc(HeII) = 0.6-0.8 but f_esc(HI) = 1 would increase the index by Delta-alpha_b = 0.3-1.0, corresponding to eta = 60-200 for beta = 1.5-1.6, in agreement with HST/COS observations at z = 2.5-2.9. The observed range of ratios, eta < 200, constrains alpha_b < 3.4 and f_esc(HeII) > 0.4. Individual AGN with softer spectra, alpha_s > 1.7, and more internal He II absorption could produce a few absorbers with eta > 300 in proximity to AGN transverse to the sight line.
The Andromeda Galaxy (M31) has been observed with the UltraViolet Imaging Telescope (UVIT) instrument onboard the AstroSat Observatory. The M31 sky area was covered with 19 fields, in multiple UV filters per field, over the period of 2017 to 2019. The entire galaxy was observed in the FUV F148W filter, and more than half observed in the NUV filters. A new calibration and data processing is described which improves the astrometry and photometry of the UVIT data. The high spatial resolution of UVIT ($simeq$1 arcsec) and new astrometry calibration ($simeq$0.2 arcsec) allow identification of UVIT sources with stars, star clusters, X-ray sources, and other source types within M31 to a much better level than previously possible. We present new results from matching UVIT sources with stars measured as part of the Pan-chromatic Hubble Andromeda Treasury project in M31.
The close relationship between the nature of the Triangulum-Andromeda (TriAnd) overdensity and the Galactic disk has become increasingly evident in recent years. However, the chemical pattern of this overdensity (R$_{GC}$ = 20 - 30 kpc) is unique and differs from what we know of the local disk. In this study, we analyze the chemical abundances of five $alpha$ elements (Mg, O, Si, Ca, and Ti) in a sample of stars belonging to the TriAnd overdensity, including stars with [Fe/H] $<$ $-$1.2, to investigate the evolution of the $alpha$ elements with metallicity. High-resolution spectra from Gemini North with GRACES were analyzed. Overall, the TriAnd population presents an $alpha$-element pattern that differs from that of the local disk; the TriAnd stars fall in between the local disk and the dwarf galaxies in the [X/Fe] vs. [Fe/H] plane. The high [Mg/Fe] ratios obtained for the lower metallicity TriAnd stars may indicate a roughly parallel sequence to the Milky Way local disk at lower values of [Fe/H], revealing a knee shifted towards lower metallicities for the TriAnd population. Similar behavior is also exhibited in the [Ca/Fe] and [Si/Fe] ratios. However, for O and Ti the behavior of the [X/Fe] ratios shows a slight decay with decreasing metallicity. Our results reinforce the TriAnd overdensity as a unique stellar population of the Milky Way, with an abundance pattern that is different from all stellar populations studied to date. The complete understanding of the complex TriAnd population will require high-resolution spectroscopic observations of a larger sample of TriAnd stars.
We study the gas distribution in the Milky Way and Andromeda using a constrained cosmological simulation of the Local Group (LG) within the context of the CLUES (Constrained Local UniversE Simulations) project. We analyse the properties of gas in the simulated galaxies at $z=0$ for three different phases: `cold, `hot and HI, and compare our results with observations. The amount of material in the hot halo ($M_{hot}approx 4-5times10^{10},$M$_{odot}$), and the cold ($M_{cold}(rlesssim10,$kpc$)approx10^{8},$M$_{odot}$) and HI ($M_{HI}(rlesssim50,$kpc$)approx 3-4times10^8,$M$_{odot}$) components display a reasonable agreement with observations. We also compute the accretion/ejection rates together with the HI (radial and all-sky) covering fractions. The integrated HI accretion rate within $r=50,$kpc gives $sim$$0.2-0.3,$M$_{odot},$yr$^{-1}$, i.e. close to that obtained from high-velocity clouds in the Milky Way. We find that the global accretion rate is dominated by hot material, although ionized gas with $Tlesssim10^5,$K can contribute significantly too. The $net$ accretion rates of $all$ material at the virial radii are $6-8,$M$_{odot},$yr$^{-1}$. At $z=0$, we find a significant gas excess between the two galaxies, as compared to any other direction, resulting from the overlap of their gaseous haloes. In our simulation, the gas excess first occurs at $zsim1$, as a consequence of the kinematical evolution of the LG.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
