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Register a new userIs there substructure around M87?
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We present a general method to identify infalling substructure in discrete datasets with position and line-of-sight velocity data. We exploit the fact that galaxies falling onto a brightest cluster galaxy (BCG) in a virialised cluster, or dwarf satellites falling onto a central galaxy like the Milky Way, follow nearly radial orbits. If the orbits are exactly radial, we show how to find the probability distribution for a satellites energy, given a tracer density for the satellite population, by solving an Abel integral equation. This is an extension of Eddington (1916)s classical formula for the isotropic distribution function. When applied to a system of galaxies, clustering in energy space can then be quantified using the Kullback-Leibler divergence, and groups of objects can be identified which, though separated in the sky, may be falling in on the same orbit. This method is tested using mock data and applied to the satellite galaxy population around M87, the BCG in Virgo, and a number of associations are found which may represent infalling galaxy groups.
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Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a diffuse interstellar medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or H~{sc ii} region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300-1800~MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby H~{sc ii} region observed at low frequencies, most of the effects of a depolarization wall are evident: the H~{sc ii} region depolarizes background emission and less (but not zero) information from beyond the H~{sc ii} region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.
The presence of a debris disc around the Gyr-old solar-type star $zeta^2,mathrm{Reticuli}$ was suggested by the $mathit{Spitzer}$ infrared excess detection. Follow-up observations with $mathit{Herschel}$/PACS revealed a double-lobed feature, that displayed asymmetries both in brightness and position. Therefore, the disc was thought to be edge-on and significantly eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which unambiguously reveal that these lobes show no common proper motion with $zeta^2,mathrm{Reticuli}$. In these observations, no flux has been detected around $zeta^2,mathrm{Reticuli}$ that exceeds the $3sigma$ levels. We conclude that surface brightness upper limits of a debris disc around $zeta^2,mathrm{Reticuli}$ are $5.7,mathrm{mu Jy/arcsec^2}$ at 1.3 mm, and $26,mathrm{mu Jy/arcsec^2}$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $mathit{Herschel}$ observations of debris discs and clarify the effects of background confusion.
We observed two fields near M32 with the ACS/HRC on board the Hubble Space Telescope, located at distances of about 1.8 and 5.4 (hereafter F1 and F2, respectively) from the center of M32. To obtain a very detailed and deep color-magnitude diagram (CMD) and to look for short period variability, we obtained time-series imaging of each field in 32-orbit-long exposures using the F435W (B) and F555W (V) filters, spanning a temporal range of 2 days per filter. We focus on our detection of variability on RR Lyrae variable stars, which represents the only way to obtain information about the presence of a very old population (larger than 10 Gyr) in M32 from optical data. Here we present results obtained from the detection of 31 RR Lyrae in these fields: 17 in F1 and 14 in F2.
As progenitors of the most massive objects, protoclusters are key to tracing the evolution and star-formation history of the Universe, and are responsible for ${gtrsim},20$ per cent of the cosmic star formation at $z,{>},2$. Using a combination of state-of-the-art hydrodynamical simulations and empirical models, we show that current galaxy-formation models do not produce enough star formation in protoclusters to match observations. We find that the star-formation rates (SFRs) predicted from the models are an order of magnitude lower than what is seen in observations, despite the relatively good agreement found for their mass-accretion histories, specifically that they lie on an evolutionary path to become Coma-like clusters at $z,{simeq}, 0$. Using a well-studied protocluster core at $z,{=},4.3$ as a test case, we find that star-formation efficiency of protocluster galaxies is higher than predicted by the models. We show that a large part of the discrepancy can be attributed to a dependence of SFR on the numerical resolution of the simulations, with a roughly factor of 3 drop in SFR when the spatial resolution decreases by a factor of 4. We also present predictions up to $z,{simeq},7$. Compared to lower redshifts, we find that centrals (the most massive member galaxies) are more distinct from the other galaxies, while protocluster galaxies are less distinct from field galaxies. All these results suggest that, as a rare and extreme population at high-$z$, protoclusters can help constrain galaxy formation models tuned to match the average population at $z,{simeq},0$.
It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here, an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA Cycle 4 data of a hot molecular core, G10.47+0.03 is utilized for this study. Various aldehydes (acetaldehyde, propanal, and glycolaldehyde), alcohols (methanol and ethylene glycol), and a ketone (acetone) are identified in this source. The excitation temperatures and the column densities of these species were derived via the rotation diagram method assuming LTE conditions. An extensive investigation is carried out to understand the formation of these species. Six pairs of aldehyde-alcohol: i) methanal and methanol; ii) ethanal and ethanol; iii) propanal and 1-propanol; iv) propenal and allyl alcohol; v) propynal and propargyl alcohol; vi) glycolaldehyde and ethylene glycol; vii) along with one pair of ketone-alcohol (acetone and isopropanol) and viii) ketene-alcohol (ethenone and vinyl alcohol) are considered for this study. Two successive hydrogenation reactions in the ice phase are examined to form these alcohols from aldehydes, ketone, and ketene, respectively. Quantum chemical methods are extensively executed to review the ice phase formation route and the kinetics of these species. Based on the obtained kinetic data, astrochemical modeling is employed to derive the abundances of these aldehydes, alcohols, ketone, and ketene in this source. It is seen that our model could successfully explain the observed abundances of various species in this hot molecular core.
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