Astrophysics of Galaxies (astro-ph.GA)

Abstract: We quantify the differences between stellar accelerations in disk galaxies formed in a MONDian universe relative to galaxies with the identical baryonic matter distributions and a fitted cold dark matter halo. In a Milky Way-like galaxy the maximal transverse acceleration is ${\cal {O}}(10^{-9})$ arcseconds per year per decade, well beyond even the most optimistic extrapolations of current capabilities. Conversely, the maximum difference in the line-of-sight acceleration is ${\cal {O}}(1)$ centimetre per second per decade at solar distances from the galactic centre. This level of precision is within reach of plausible future instruments.

Abstract: We analyze all the available Atacama Large Millimeter / submillimeter Array archival data of the nearby Type-II Seyfert galaxy NGC 1068, including new 100 GHz data with the angular resolution of 0\farcs05, which was not included in previous continuum spectral analysis. By combining with the literature data based on the Very Large Array, we investigate the broadband radio continuum spectrum of the central $\lesssim7$ pc region of NGC 1068. We found that the flux density is between $\approx$10-20 mJy at 5-700 GHz. Due to the inability of the model in previous studies to account for the newly added 100 GHz data point, we proceeded to update the models and make the necessary adjustments to the parameters. One possible interpretation of this broadband radio spectrum is a combination of emission from the jet base, the dusty torus, and the compact X-raying corona with the magnetic field strength of $\approx20$ G on scales of $\approx30$ Schwarzschild radii from the central black hole. In order to firmly identify the compact corona by omitting any other possible extended components (e.g., free-free emission from ionized gas around), high-resolution/sensitivity observations achieved by next-generation interferometers will be necessary.

Abstract: We examine spatial variations of the C$^0$/CO abundance ratio ($X_{\mathrm{C/CO}}$) in the vicinity of the $\gamma$-ray supernova remnant W51C, based on [CI] ($^3P_1$-$^3P_0$), $^{12}$CO(1-0), and $^{13}$CO(1-0) observations with the ASTE and Nobeyama 45-m telescopes. We find that $X_{\mathrm{C/CO}}$ varies in a range of 0.02-0.16 (0.05 in median) inside the molecular clouds of $A_V>$100 mag, where photodissociation of CO by the interstellar UV is negligible. Furthermore, $X_{\mathrm{C/CO}}$ is locally enhanced up to by a factor of four near the W51C center, depending on the projected distance from the W51C center. In high-$A_V$ molecular clouds, $X_{\mathrm{C/CO}}$ is determined by the ratio of the cosmic-ray (CR) ionization rate to the H$_2$ density, and we find no clear spatial variation of the H$_2$ density against the projected distance. Hence, the high CR ionization rate may locally enhance $X_{\mathrm{C/CO}}$ near the W51C center. We also find that the observed spatial extent of the enhanced $X_{\mathrm{C/CO}}$ ($\sim$17 pc) is consistent with the diffusion distance of CRs with the energy of 100 MeV. The fact suggests that the low-energy CRs accelerated in W51C enhance $X_{\mathrm{C/CO}}$. The CR ionization rate at the $X_{\mathrm{C/CO}}$-enhanced cloud is estimated to be 3$\times$10$^{-16}$ s$^{-1}$ on the basis of time-dependent PDR simulations of $X_{\mathrm{C/CO}}$, the value of which is 30 times higher than that in the standard Galactic environment. These results demonstrate that [CI] is a powerful probe to investigate the interaction between CRs and the interstellar medium for a wide area in the vicinity of supernova remnants.

Abstract: We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and SST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A1489. These SMA-located sources both lie at z=4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam observations. We investigate their stellar, ISM, and dynamical properties, including a pixel-level SED analysis to derive sub-kpc-resolution stellar-mass and Av maps. We find that 850.1 is one of the most massive and highly obscured, Av~5, galaxies known at z>4 with M*~10^11.8 Mo (likely forming at z>6), and 850.2 is one of the least massive and least obscured, Av~1, members of the z>4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z>3-4 based on imaging at <2um, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar mass distribution, Re(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches both the properties of massive, quiescent galaxies at z~1.5 and ultra-massive early-type galaxies at z~0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature which we link to the active dynamical environment it resides within.

Abstract: We use the Galaxy and Mass Assembly (GAMA) and the Deep Extragalactic Visible Legacy Survey (DEVILS) observational data sets to calculate the cosmic star formation rate (SFR) and active galactic nuclei (AGN) bolometric luminosity history (CSFH/CAGNH) over the last 12.5 billion years. SFRs and AGN bolometric luminosities were derived using the spectral energy distribution fitting code ProSpect, which includes an AGN prescription to self consistently model the contribution from both AGN and stellar emission to the observed rest-frame ultra-violet to far-infrared photometry. We find that both the CSFH and CAGNH evolve similarly, rising in the early Universe up to a peak at look-back time $\approx 10$~Gyr ($z \approx 2$), before declining toward the present day. The key result of this work is that we find the ratio of CAGNH to CSFH has been flat ($\approx 10^{42.5}\mathrm{erg \, s^{-1}M_{\odot}^{-1}yr}$) for $11$~Gyr up to the present day, indicating that star formation and AGN activity have been coeval over this time period. We find that the stellar masses of the galaxies that contribute most to the CSFH and CAGNH are similar, implying a common cause, which is likely gas inflow. The depletion of the gas supply suppresses cosmic star formation and AGN activity equivalently to ensure that they have experienced similar declines over the last 10 Gyr. These results are an important milestone for reconciling the role of star formation and AGN activity in the life cycle of galaxies.

Abstract: We extend the study of the radio emission in early-type galaxies (ETGs) in the nearby Universe (recession velocity <7,500 km/s) as seen by the 150 MHz Low-Frequency ARray (LOFAR) observations and extend the sample from giant ETGs to massive (~6x10^10 - 3x10^11 solar masses) ETGs (mETGS) with -25 < MK < -23.5. Images from the second data release of the LOFAR Two-metre Sky Survey were available for 432 mETGs, 48% of which are detected above a typical luminosity of ~3x10^20 W/Hz. Most (85%) of the detected sources are compact, with sizes <4 kpc. The radio emission of 31 mETGs is extended on scales ranging from 2 to 180 kpc (median 12 kpc). In several cases, it is aligned with the host galaxy. We set a limit of ~1% to the fraction of remnant or restarted objects, which is ~16% of the extended sources. We found that the properties of the radio sources are connected with the stellar mass of the ETGs (the median radio power, the fraction of extended radio sources, and the link with the large-scale environment). However, these results only describe statistical trends because the radio properties of sources of similar stellar mass and environment show a large spread of radio properties. These trends break at the lowest host luminosities (MK>-24.5). This effect is strengthened by the analysis of even less massive ETGs, with -23.5 < MK < -21.5. This suggests that at a mass of ~2x10^11 solar masses, a general transition occurs from radio emission produced from radio-loud active galactic nuclei (AGN) to processes related to the host galaxy and (or) radio quiet AGN. At this luminosity, a transition in the stellar surface brightness profile also occurs from Sersic galaxies to those with a depleted stellar core, the so-called core galaxies. This finding is in line with previous results that indicated that only core galaxies host radio-loud AGN.