Astrophysics of Galaxies (astro-ph.GA)

Abstract: We separately assess elemental abundances in AGNs' broad and narrow emission line regions (BLR and NLR), based on a critical assessment of published results together with new photoionization models. We find 1) He/H enhancements in some AGN, exceeding what can be explained by normal chemical evolution and confirm 2) super-solar {\alpha} abundance, though to a lesser degree than previously reported. We also reaffirm 3) a N/O ratio consistent with secondary production; 4) solar or slightly sub-solar Fe abundance; and 5) red-shift independent metallicity, in contrast with galactic chemical evolution. We interpret 6) the larger metallicity in the BLR than NRL in terms of an in situ stellar evolution and pollution in AGN discs (SEPAD) model. We attribute: a) the redshift independence to the heavy element pollutants being disposed into the disc and accreted onto the central supermassive black hole (SMBH); b) the limited He excess to the accretion-wind metabolism of a top-heavy population of evolving massive main sequence stars; c) the super-solar CNO enrichment to the nuclear synthesis during their post-main-sequence evolution; d) the large N/O to the byproduct of multiple stellar generations; and e) the Mg, Si, and Fe to the ejecta of type II supernovae in the disc. These results provide supporting evidence for f) ongoing self-regulated star formation, g) adequate stellar luminosity to maintain marginal gravitational stability, h) prolific production of seeds and i) dense coexistence of subsequently-grown residual black hole populations in AGN discs.

Abstract: We report on further observations of the field of the quasar Q1218+0832. Geier et al. (2019) presented the discovery of the quasar resulting from a search for quasars reddened and dimmed by dust in foreground Damped Lyman-alpha Absorbers (DLAs). The DLA is remarkable by having a very large HI column density close to 10^22 cm^-2. Its dust extinction curve shows the 2175 AA-bump known from the Local Group. It also shows absorption from cold gas exemplified by CI and CO-molecules. We here present narrow-band observations of the field of Q1218+0832 and also use archival HST image to search for the galaxy counterpart of the DLA. No emission from the DLA galaxy is found neither in the narrow-band imaging nor in the HST image. In the HST image, we can probe down to an impact parameter of 0.3 arcsec and a 3-sigma detection limit of 26.8 mag per arcsec^2. In the narrow-band image, we probe down to 0 arcsec impact parameter and detect nothing down to a 3-sigma detection limit of about 3*10^-17 erg s^-1 cm^-2. We do detect a bright Lyman-alpha emitter 59 arcsec south of Q1218+0832 with a flux of 3*10^-16 erg s^-1 cm^-2. We conclude that the DLA galaxy must be located at very small impact parameter (<0.3 arcsec, 2.5 kpc) or is optically dark. Also, the DLA galaxy most likely is part of a galaxy group.

Abstract: We present an analysis of the detection fraction and the number counts of radio sources imaged with Very Long Baseline Interferometry (VLBI) at 1.4 GHz as part of the mJIVE-20 survey. From a sample of 24,903 radio sources identified by FIRST, 4,965 are detected on VLBI-scales, giving an overall detection fraction of $19.9\pm2.9~$per cent. However, we find that the detection fraction falls from around 50 per cent at a peak surface brightness of $80~mJy~beam^{-1}$ in FIRST to around 8 per cent at the detection limit, which is likely dominated by the surface brightness sensitivity of the VLBI observations, with some contribution from a change in the radio source population. We also find that compactness at arcsec-scales is the dominant factor in determining whether a radio source is detected with VLBI, and that the median size of the VLBI-detected radio sources is 7.7 mas. After correcting for the survey completeness and effective sky area, we determine the slope of the differential number counts of VLBI-detected radio sources with flux densities $S_{\rm 1.4~GHz} > 1~mJy$ to be $\eta_{\rm VLBI} = -1.74\pm 0.02$, which is shallower than in the cases of the FIRST parent population ($\eta_{\rm FIRST} = -1.77\pm 0.02$) and for compact radio sources selected at higher frequencies ($\eta_{\rm JBF} = -2.06\pm 0.02$). From this, we find that all-sky ($3\pi~sr$) surveys with the EVN and the VLBA have the potential to detect $(7.2\pm0.9)\times10^{5}$ radio sources at mas-resolution, and that the density of compact radio sources is sufficient (5.3~deg$^{-2}$) for in-beam phase referencing with multiple sources (3.9 per primary beam) in the case of a hypothetical SKA-VLBI array.

Abstract: The majority of baryons, which account for $15\%$ of the matter in the Universe, will end their lives as carbon and oxygen inside cold black dwarfs. Dark matter (DM) makes up the remaining $85\%$ of the matter in the universe, however, the fate of DM is unknown. Here we show that the destiny of purely gravitationally interacting DM particles follows one of two possible routes. The first possible route, the "radiation-destiny" scenario, is that massive DM particles lose sufficient energy through gravitational radiation causing them to spiral into a supermassive black hole that ultimately disappears through Hawking radiation. The second possible route, the "drifting-alone" destiny, applies to lighter DM particles, where only the central DM halo region spirals into the central BH which is then Hawking radiated away. The rest of the DM halo is ripped apart by the accelerated expansion of the Universe.

Abstract: We report the detection of large hydrocarbon cycles toward several cold dense clouds. We observed four sources (L1495B, Lupus-1A, L483, and L1527) in the Q band (31-50 GHz) using the Yebes 40m radiotelescope. Using the line stack technique, we find statistically significant evidence of benzonitrile (C6H5CN) in L1495B, Lupus-1A, and L483 at the 31.8 sigma, 15.0 sigma, and 17.2 sigma levels, respectively, while there is no hint of C6H5CN in the fourth source, L1527. The column densities derived are in the range (1.8-4.0)e12 cm-2, which is somewhat below the value derived toward the cold dense cloud TMC-1. When we analyse together all the benzonitrile abundances derived toward cold clouds in this study and in the literature, a clear trend emerges in which the higher the abundance of HC7N, the more abundant C6H5CN is. This indicates that aromatic cycles are specially favored in those interstellar clouds where long carbon chains are abundant, which suggests that the chemical processes that are responsible for the formation of linear carbon chains are also behind the synthesis of aromatic rings. We also searched for cycles other than benzonitrile, and found evidence of indene (C9H8), cyclopentadiene (C5H6), and 1-cyano cyclopentadiene (1-C5H5CN) at the 9.3 sigma, 7.5 sigma, and 8.4 sigma, respectively, toward L1495B, which shows the strongest signal from C6H5CN. The relative abundances between the various cycles detected in L1495B are consistent, within a factor of three, to those found previously in TMC-1. It is therefore likely that not only C6H5CN but also other large aromatic cycles are abundant in clouds rich in carbon chains.

Abstract: We present VLT/MUSE observations targeting the extended Lyman-$\alpha$ (Ly$\alpha$) emission of five high-redshift ($z\sim$3-4) submillimeter galaxies (SMGs) with increasing quasar (QSO) radiation: two SMGs, two SMGs hosting a QSO, and one SMG hosting a QSO with a SMG companion (QSO+SMG). These sources should be located in dark matter halos of comparable masses (average mass of $M_{\rm DM}\sim10^{12.2}\,{\rm M}_\odot$). We quantify the luminosity and extent of the Ly$\alpha$ emission, together with its kinematics, and examine four Ly$\alpha$ powering mechanisms: photoionization from QSOs/star formation, shocks by galactic/QSO outflows, gravitational cooling radiation, and Ly$\alpha$ photons resonant scattering. We find a variety of Ly$\alpha$ luminosities and extents, with the QSO+SMG system displaying the most extended and bright nebula, followed by the SMGs hosting a QSO, and finally the undetected circumgalactic medium (CGM) of SMGs. This diversity implies that gravitational cooling is unlikely to be the main powering mechanism. We show that photoionization from the QSO and QSO outflows can contribute to power the emission for average densities $n_{\rm H}>0.5\,$cm$^{-3}$. Moreover, the observed Ly$\alpha$ luminosities scale with the QSO's budget of Ly$\alpha$ photons modulo the dust content in each galaxy, highlighting a possible contribution from resonant scattering of QSO's radiation in powering the nebulae. We find larger Ly$\alpha$ linewidths (FWHM$\gtrsim 1200\,$km$\,$s$^{-1}$) than usually reported around radio-quiet systems, pointing to large-scale outflows. A statistical survey targeting similar high-redshift massive systems with known host properties is needed to confirm our findings.

Abstract: In this paper we investigate the role of AGN feedback on the late stage evolution of elliptical galaxies by performing high-resolution hydrodynamical simulation in the {\it MACER} framework. By comparing models that take into account different feedback mechanisms, namely AGN and stellar feedback, we find that AGN feedback is crucial in keeping the black hole in a low accretion state and suppressing the star formation. We then compare the energy from AGN radiation and wind deposited in the galaxy and find that only wind can compensate for the radiative cooling of the gas in the galaxy. Further, we investigate which plays the dominant role, the wind from the cold (quasar) or hot (radio) feedback modes, by examining the cumulative energy output and impact area to which the wind can heat the interstellar medium and suppress star formation. Our results indicate that first, although AGN spends most of its time in hot (radio) mode, the cumulative energy output is dominated by the outburst of the cold mode. Second, only the impact area of the cold-mode wind is large enough to heat the gas in the halo, while the hot-mode wind is not. Additionally, the cold-mode wind is capable of sweeping up the material from stellar mass loss. These results indicate the dominant role of cold-mode wind. The limitations of our model, including the absence of jet feedback, are discussed.

Abstract: The proto-Milky Way epoch forms the earliest stars in our Galaxy and sets the initial conditions for subsequent disk formation. Recent observations from APOGEE and H3 surveys showed that the [$\alpha$/Fe] ratio slowly declined between [Fe/H] $=-3$ and $-1.3$ until it reached the lowest value ($\sim 0.25$) among the selected in situ metal-poor stars that most likely formed during the proto-Galaxy epoch. [$\alpha$/Fe] rose to meet the traditional high value commonly associated with the thick disk population at [Fe/H] $=-1$. It was suggested that the rise in [$\alpha$/Fe] could be caused by an increase in the star formation efficiency (SFE), known as the "simmering" phase scenario. However, gas inflow also plays a vital role in shaping the star formation history and chemical evolution of galaxies. We investigate this unexpected [$\alpha$/Fe]-rise with a statistical experiment involving a galactic chemical evolution (GCE). Our model has five free parameters: the mass of the initial reservoir of the cold interstellar medium (ISM) at birth, the frequency of Type Ia supernovae (SNe Ia), the cooling timescale of the warm ISM, the SFE, and the inflow rate of fresh gas. The last two free parameters were allowed to change after [$\alpha$/Fe] reached its lowest value, dividing the proto-Galaxy epoch into two phases. We find that the rise in [$\alpha$/Fe] is caused by a large inflow of fresh gas and conclude that the [$\alpha$/Fe]-rise is a signature of the cold mode accretion whose materials formed the prototype Milky Way preceding disk formation. Although the SFE is essential in regulating the chemical evolution, it does not necessarily increase to facilitate the [$\alpha$/Fe]-rise.

Abstract: We report JWST NIRCam observations of G0.253+0.015, the molecular cloud in the Central Molecular Zone known as The Brick, with the F182M, F187N, F212N, F410M, F405N, and F466N filters. We catalog 56,146 stars detected in all 6 filters using the crowdsource package. Stars within and behind The Brick exhibit prodigious absorption in the F466N filter that is produced by a combination of CO ice and gas. In support of this conclusion, and as a general resource, we present models of CO gas and ice and CO$_2$ ice in the F466N, F470N, and F410M filters. Both CO gas and ice may contribute to the observed stellar colors. We show, however, that CO gas does not absorb the Pf$\beta$ and Hu$\epsilon$ lines in F466N, but that these lines show excess absorption, indicating that CO ice is also present and contributes to observed F466N absorption. The most strongly absorbed stars in F466N are extincted by $\sim$ 2 magnitudes, corresponding to $>$ 80\% flux loss. This high observed absorption requires very high column densities of CO, requiring total CO column that is in tension with standard CO abundance and/or gas-to-dust ratios. There is therefore likely to be a greater CO/H$_2$ ratio (X$_{CO} > 10^{-4}$) and more dust per H$_2$ molecule ($>0.01$) in the Galactic Center than the Galactic disk. Ice and/or gas absorption is observed even in the cloud outskirts, implying that additional caution is needed when interpreting stellar photometry in filters that overlap with ice bands throughout our Galactic Center. The widespread CO absorption in our Galactic Center hints that significant ice absorption is likely present in other galactic centers.

Abstract: We present a study of the morphology of star formation and the associated nuclear activity in a sample of 8 closely interacting southern galaxies, which are in different stages of interaction, starting with nearly merged nuclei that have one prominent bulge to more widely spaced interacting galaxies. We have used Far-Ultraviolet (FUV) observations from the Ultraviolet Imaging telescope (UVIT), near-Infrared observations from the infrared survey facility telescope (IRSF) and archival optical data from the VLT/MUSE integral field spectrograph. Analysing resolved stellar populations across the disk of the interacting galaxies can provide unique insights into how interactions affect galaxy properties, such as morphology, star formation rates and chemical composition. We take advantage of the unprecedented capabilities of MUSE and UVIT to carry out a highly detailed spatially and spectrally resolved study of star formation rate, star formation histories, metallicity and AGN activity in the sample of eight interacting galaxies which are in different stages of interaction. Most of our sample galaxies are gas-rich and show evidence of recent, massive star formation in tidal tails, rings and spiral arms. This is evident from their FUV and H$\alpha$ emissions, which trace young, massive star-forming regions. We compared the star formation rate in the barred and unbarred galaxies in our sample and found that the barred galaxies do not show significant enhancement in star formation rate or large-scale difference in star formation morphology compared to unbarred galaxies. IC5250 and NGC7733N, show extended nuclear outflows of size $\sim$ 5 kpc and 8 kpc respectively.