Astrophysics of Galaxies (astro-ph.GA)

Abstract: Cyanides, ranging from three carbon atoms to PAHs, and alkenyl compounds are abundant in the interstellar medium (ISM). Aminoacrylonitrile (3-Amino-2-propenenitrile, H$_{2}$N-CH=CH-CN), an alkenyl cyanide, thus represents a promising candidate for new interstellar detection. A comprehensive spectroscopic laboratory investigation of aminoacrylonitrile in its rotational ground vibrational state has been herein performed. The measurements carried out up to the THz regime made it possible to generate a precise set of reliable rest frequencies for its search in space up to sub-millimetre wavelengths. The $Z$-aminoacrylonitrile ($Z$-apn) isomer spectrum has been recorded employing a source-modulated sub-millimetre spectrometer, from 80 GHz to 1 THz. A combination of Doppler and sub-Doppler measurement regimes allowed to record 600 new lines. The collected data have enabled the characterisation of a set of spectroscopic parameters up to decic centrifugal distortion constants. The catalogue generated from the improved spectral data has been used for the search of $Z$-apn in the spectral survey of the G+0.693-0.027 molecular cloud located in the central molecular zone, in the proximity of the Galactic centre.

Abstract: We present a multi-scale and multi-wavelength study to unveil massive star formation (MSF) processes around sites AFGL 5180, and AFGL 6366S, both hosting a Class II 6.7 GHz methanol maser emission. The radio continuum map at 8.46 GHz reveals a small cluster of radio sources toward AFGL 5180. Signatures of the early stages of MSF in our target sites are spatially seen at the opposite edges of a filamentary cloud (length $\sim$5 pc), which is observed in the sub-millimeter dust continuum maps. Using the near-infrared photometric data, the spatial distribution of young stellar objects is found toward the entire filament, primarily clustered at its edges. The getsf utility on the Herschel far-infrared images reveals a hub-filament system (HFS) toward each target site. The analysis of the molecular line data, which benefits from large area coverage ($\sim$1 degree $\times$ 1 degree), detects two cloud components with a connection in both position and velocity space. This supports the scenario of a cloud-cloud collision (CCC) that occurred $\sim$1 Myr ago. The filamentary cloud, connecting AFGL 5180 and AFGL 6366S, seems spatially close to an HII region Sh2-247 excited by a massive O9.5 star. Based on the knowledge of various pressures exerted by the massive star on its surroundings, the impact of its energetic feedback on the filamentary cloud is found to be insignificant. Overall, our observational outcomes favor the possibility of the CCC scenario driving MSF and the formation of HFSs toward the target sites.

Abstract: Wide-field radio continuum observations of galaxy clusters are revealing an increasing number of spiral galaxies hosting tens of kpc-long radio tails produced by the nonthermal interstellar medium being displaced by the ram pressure. We present a semi-empirical model for the multi-frequency radio continuum emission from ram pressure stripped tails based on the pure synchrotron cooling of a radio plasma moving along the stripping direction with a uniform velocity. We combine LOFAR and uGMRT observations at 144 and 400 MHz to study the flux density and spectral index profiles of the radio tails of 7 galaxies in Abell 2255, and use the model to reproduce the flux density and spectral index profiles, and infer the stripped radio plasma velocity. For 5 out of 7 galaxies we observe monotonic decrease in both flux density and spectral index up to $~30$ kpc from their stellar disk. Our model reproduces the observed trends with a radio plasma bulk projected velocity between 160 and 430 km s$^{-1}$. This result represents the first indirect measure of the stripped, nonthermal interstellar medium velocity. The observed spectral index trends indicate that the synchrotron cooling is faster than the adiabatic expansion losses, thus suggesting that the stripped radio plasma can survive for a few tens of Myr outside of the stellar disk. This provides a lower limit for the lifetime of the stripped ISM outside of the disk. As a proof of concept, we use the best-fit velocities to constrain the galaxies' 3D velocity in the cluster to be in the 300-1300 km s$^{-1}$. We estimate the ram pressure affecting these galaxies to be between 0.1 and 2.9 $\times10^{-11}$ erg cm$^{-3}$, and measure the inclination between their stellar disk and the ram pressure wind.

Abstract: Galaxies have been observed to exhibit a level of simplicity unexpected in the complex galaxy formation scenario posited by standard cosmology. This is particularly apparent in their dynamics, where scaling relations display much regularity and little intrinsic scatter. However, the parameters responsible for this simplicity have not been identified. Using the Spitzer Photometry & Accurate Rotation Curves galaxy catalogue, we argue that the radial acceleration relation (RAR) between galaxies' baryonic and total dynamical accelerations is the fundamental correlation governing the radial (in-disk) dynamics of late-type galaxies. In particular, we show that the RAR cannot be tightened by the inclusion of any other available galaxy property, that it is the strongest projection of galaxies' radial dynamical parameter space, and that all other statistical radial dynamical correlations stem from the RAR plus the non-dynamical correlations present in our sample. We further provide evidence that the RAR's fundamentality is unique in that the second most significant dynamical relation does not possess any of these features. Our analysis reveals the root cause of the correlations present in galaxies' radial dynamics: they are nothing but facets of the RAR. These results have important ramifications for galaxy formation theory because they imply that to explain statistically late-type galaxy dynamics within the disk it is necessary and sufficient to explain the RAR and lack of any significant, partially independent correlation. While simple in some modified dynamics models, this poses a challenge to standard cosmology.

Abstract: In this paper we will present findings on the detection of Magnesium II (MgII, lambda = 2796 {\AA}, 2803 {\AA}) absorption systems observed in data from the Early Data Release (EDR) of the Dark Energy Spectroscopic Instrument (DESI). DESI is projected to obtain spectroscopy of approximately 3 million quasars (QSOs), of which over 99% are anticipated to be found at redshifts greater than z < 0.3, such that DESI would be able to observe an associated or intervening Mg II absorber illuminated by the background QSO. We have developed an autonomous supplementary spectral pipeline that detects such systems through an initial line-fitting process and then confirms line properties using a Markov Chain Monte Carlo (MCMC) sampler. Based upon both a visual inspection and the reanalysis of coadded observations, we estimate this sample of absorption systems to have a completeness of 82.56% and purity of 99.08%. As the spectra in which Mg II systems are detected are the result of coadding multiple observations, we can determine the sensitivity, and therefore completeness, of the sample by searching for known Mg II systems in coadded data with fewer observations (and therefore lower signal-to-noise). From a parent catalog containing 83,207 quasars, we detect a total of 23,921 Mg II absorption systems following a series of quality cuts. Extrapolating from this occurrence rate of 28.75% implies a catalog at the completion of the five-year DESI survey that contains over eight hundred thousand Mg II absorbers. The cataloging of these systems will enable significant further research as they carry information regarding circumgalactic medium (CGM) environments, the distribution of intervening galaxies, and the growth of metallicity across the redshift range 0.3 < z < 2.5.

Abstract: Dust is important for star formation because it is the crucial component that couples gas to stellar radiation fields, allowing radiation feedback to influence gas fragmentation and thus the stellar initial mass function (IMF). Variations in dust abundance therefore provide a potential avenue by which variation in galaxy metallicity might affect the IMF. In this paper we present a series of radiation-magnetohydrodynamic simulations in which we vary the metallicity and thus the dust abundance from 1% of Solar to 3$\times$ Solar, spanning the range from the lowest metallicity dwarfs to the most metal-rich early-type galaxies found in the local Universe. We design the simulations to keep all dimensionless parameters constant so that the interaction between feedback and star-forming environments of varying surface density and metallicity is the only factor capable of breaking the symmetry between the simulations and modifying the IMF, allowing us to cleanly isolate and understand the effects of each environmental parameter. We find that at a fixed surface density more metal-rich clouds tend to form a slightly more bottom-heavy IMF than metal-poor ones, primarily because in metal-poor gas radiation feedback is able to propagate further, heating somewhat larger volumes of gas. However, shifts in IMF with metallicity at a fixed surface density are much smaller than shifts with surface density at fixed metallicity; metallicity-induced IMF variations are too small to explain the variations in mass-to-light ratio reported in galaxies of different mass and metallicity. We, therefore, conclude that metallicity variations are much less important than variations in surface density in driving changes in the IMF and that the latter rather than the former are most likely responsible for the IMF variations found in early-type galaxies.