Astrophysics of Galaxies (astro-ph.GA)

Abstract: RAFGL2591 is a massive star-forming complex in the Cygnus-X region comprising of a cluster of embedded protostars and young stellar objects located at a distance of 3.33 kpc. We investigate low-frequency radio emission from the protostellar jet associated with RAFGL2591 using the Giant Metrewave Radio Telescope (GMRT) at 325, 610 and 1280 MHz. For the first time, we have detected radio jet lobes in the E-W direction, labelled as GMRT-1 and GMRT-2. While GMRT-1 displays a flat radio spectral index of $\alpha$ = -0.10 , GMRT-2 shows a steeply negative value $\alpha$ = -0.62 suggestive of non-thermal emission. H$_2$ emission maps show the presence of numerous knots, arcs and extended emission towards the East-West jet, excited by the protostar VLA 3. In addition, we report a few H$_2$ knots in the North-East and South-West for the first time. The radio lobes (GMRT-1, GMRT-2) and H$_2$ emission towards this region are understood in the context of the prominent East-West jet as well as its lesser-known sibling jet in the North-East and South-West direction. To model the radio emission from the lobes, we have employed a numerical model including both thermal and non-thermal emission and found number densities towards these lobes in the range 100 - 1000 cm$^{-3}$ . The misalignment of the East-West jet lobes exhibits a reflection symmetry with a bending of $\sim$ 20$\circ$ . We attempt to understand this misalignment through precession caused by a binary partner and/or a supersonic side wind from source(s) in the vicinity.

Abstract: We introduce a new chemical enrichment and stellar feedback model into GIZMO, using the SIMBA sub-grid models as a base. Based on the state-of-the-art chemical evolution model of Kobayashi et al., SIMBA-C tracks 34 elements from H$\rightarrow$Ge and removes SIMBA's instantaneous recycling approximation. Furthermore, we make some minor improvements to SIMBA's base feedback models. SIMBA-C provides significant improvements on key diagnostics such as the knee of the $z=0$ galaxy stellar mass function, the faint end of the main sequence, and the ability to track black holes in dwarf galaxies. SIMBA-C also matches better with recent observations of the mass-metallicity relation at $z=0,2$. By not assuming instantaneous recycling, SIMBA-C provides a much better match to galactic abundance ratio measures such as [O/Fe] and [N/O]. SIMBA-C thus opens up new avenues to constrain feedback models using detailed chemical abundance measures across cosmic time.

Abstract: We measure the [${\alpha}$/Fe] abundances for 183 quiescent galaxies at z = 0.60 - 0.75 with stellar masses ranging 10.4 \leq log10 10.4 $\leq$ log10 (M$_*$ /M$_\odot$) $\leq$ 11.6 selected from the LEGA-C survey. We estimate [${\alpha}$/Fe] from the ratio of the spectral indices Mgb (${\lambda} \sim 5177$ {\AA}) and Fe4383, compared to predictions of simple stellar population models. We find that 91% of quiescents in our sample have supersolar [${\alpha}$/Fe], with an average value of [${\alpha}$/Fe] = +0.24 $\pm$ 0.01. We find no significant correlation between [${\alpha}$/Fe] and stellar metallicity, mass, velocity dispersion, and average formation time. Galaxies that formed the bulk of their stellar mass on time scales shorter than 1 Gyr follow the same [${\alpha}$/Fe] distribution as those which formed on longer time scales. In comparison to local early-type galaxies and to stacked spectra of quiescent galaxies at z = 0.38 and z = 0.07, we find that the average [${\alpha}$/Fe] has not changed between z = 0.75 and the present time. Our work shows that the vast majority of massive quiescent galaxies at z $\sim$ 0.7 are ${\alpha}$-enhanced, and that no detectable evolution of the average [${\alpha}$/Fe] has taken place over the last $\sim$ 6.5 Gyr.

Abstract: We present ALMA [C II] 158 $\mu \rm{m}$ and dust continuum observations of the $z=6.79$ quasar J0109--3047 at a resolution of $0."045$ ($\sim$300 pc). The dust and [C II] emission are enclosed within a $\sim 500\, \rm{pc}$ radius, with the central beam ($r<144\ \rm{pc}$) accounting for $\sim$25\% (8\%) of the total continuum ([C II]) emission. The far--infrared luminosity density increases radially from $\sim$5 $\times 10^{11} L_\odot\ \rm{kpc}^{-2}$ to a central value of $\sim$70 $\times 10^{11} L_\odot\ \rm{kpc}^{-2}$ (SFRD $\sim$50-700 $M_\odot\ \rm{yr}^{-1}\ \rm{kpc}^{-2}$). The [C II] kinematics are dispersion-dominated with a constant velocity dispersion of $137 \pm 6 \,\rm{km\ s}^{-1}$. The constant dispersion implies that the underlying mass distribution is not centrally peaked, consistent with the expectations of a flat gas mass profile. The lack of an upturn in velocity dispersion within the central beam is inconsistent with a black hole mass greater than $M_{\rm{BH}}<6.5\times 10^{8}\ M_\odot\ (2\sigma$ level), unless highly fine-tuned changes in the ISM properties conspire to produce a decrease of the gas mass in the central beam comparable to the black hole mass. Our observations therefore imply either that a) the black hole is less massive than previously measured or b) the central peak of the far-infrared and [C II] emission are not tracing the location of the black hole, as suggested by the tentative offset between the near-infrared position of the quasar and the ALMA continuum emission.

Abstract: We universally search for evidence of kinematic and spatial correlation of supernova remnant (SNR) and molecular cloud (MC) associations for nearly all SNRs in the coverage of the MWISP CO survey, i.e. 149 SNRs, 170 SNR candidates, and 18 pure pulsar wind nebulae (PWNe) in 1 deg < l < 230 deg and -5.5 deg < b < 5.5 deg. Based on high quality and unbiased 12CO/13CO/C18O (J = 1--0) survey data, we apply automatic algorithms to identify broad lines and spatial correlations for molecular gas in each SNR region. The 91 percent of SNR-MC associations detected previously are identified in this paper by CO line emission. Overall, there could be as high as 80 percent of SNRs associated with MCs. The proportion of SNRs associated with MCs is high within the Galactic longitude less than ~50 deg. Kinematic distances of all SNRs that are associated with MCs are estimated based on systemic velocities of associated MCs. The radius of SNRs associated with MCs follows a lognormal distribution, which peaks at ~8.1 pc. The progenitor initial mass of these SNRs follows a power-law distribution with an index of ~-2.3 that is consistent with the Salpeter index of -2.35. We find that SNR-MC associations are mainly distributed in a thin disk along the Galactic plane, while a small amount distributed in a thick disk. With the height of these SNRs from the Galactic plane below ~45 pc, the distribution of the average radius relative to the height of them is roughly flat, and the average radius increases with the height when above ~45 pc.

Abstract: Thick disks are a prevalent feature observed in numerous disk galaxies including our own Milky Way. Their significance has been reported to vary widely, ranging from a few to 100% of the disk mass, depending on the galaxy and the measurement method. We use the NewHorizon simulation which has high spatial and stellar mass resolutions to investigate the issue of thick disk mass fraction. We also use the NewHorizon2 simulation that was run on the same initial conditions but additionally traced nine chemical elements. Based on a sample of 27 massive disk galaxies with M* > 10^10 M_{\odot} in NewHorizon, the contribution of the thick disk was found to be 34 \pm 15% in r-band luminosity or 48 \pm 13% in mass to the overall galactic disk, which seems in agreement with observational data. The vertical profiles of 0, 22, and 5 galaxies are best fitted by 1, 2, or 3 sech2 components, respectively. The NewHorizon2 data show that the selection of thick disk stars based on a single [{\alpha}/Fe] cut is severely contaminated by stars of different kinematic properties while missing a bulk of kinematically thick disk stars. Vertical luminosity profile fits recover the key properties of thick disks reasonably well. The majority of stars are born near the galactic mid-plane with high circularity and get heated with time via fluctuation in the force field. Depending on the star formation and merger histories, galaxies may naturally develop thick disks with significantly different properties.

Abstract: The cold dark matter (CDM) model predicts galaxies have 100 times more dark matter mass than stars. Nevertheless, recent observations report the existence of dark-matter-deficient galaxies with less dark matter than expected. To solve this problem, we investigate the physical processes of galaxy formation in head-on collisions between gas-containing dark matter subhaloes (DMSHs). Analytical estimation of the collision frequency between DMSHs associated with a massive host halo indicates that collisions frequently occur within 1/10th of the virial radius of the host halo, with a collision timescale of about 10 Myr, and the most frequent relative velocity increases with increasing radius. Using analytical models and numerical simulations, we show the bifurcation channel of the formation of dark-matter-dominated and dark-matter-deficient galaxies. In the case of low-velocity collisions, a dark-matter-dominated galaxy is formed by the merging of two DMSHs. In the case of moderate-velocity collisions, the two DMSHs penetrate each other. However the gas medium collides, and star formation begins as the gas density increases, forming a dwarf galaxy without dark matter at the collision surface. In the case of high-velocity collisions, shock-breakout occurs due to the shock waves generated at the collision surface reaching the gas surface, and no galaxy forms. For example, the simulation demonstrates that a pair of DMSHs with a mass of 10^9 Msun containing gas of 0.1 solar metallicity forms a dark-matter-deficient galaxy with a stellar mass of 10^7 Msun for a relative velocity of 200 km/s.

Abstract: Observations of high-redshift galaxies provide a critical direct test to the theories of early galaxy formation, yet to date, only four have been spectroscopically confirmed at $z>12$. Due to strong gravitational lensing over a wide area, the galaxy cluster field Abell~2744 is ideal for searching for the earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a robust detection at $z = 12.40$, and a plausible candidate at $z = 13.08$. The galaxies are discovered in JWST/NIRCam imaging and their distances are inferred with JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using JWST NIRCam and NIRSpec data corroborates the primeval characteristics of these galaxies: low mass ($\sim 10^8 ~{\rm M_\odot}$), young, rapidly-forming, metal-poor, and star-forming. Interestingly, both galaxies are spatially resolved, having lensing-corrected rest-UV effective radii on the order of 300--400 pc. These sizes are notably larger than other $z>10$ systems, implying significant scatter in the size-mass relation at early times. Deep into the epoch of reionization, these discoveries elucidate the emergence of the first galaxies.

Abstract: Context. The advent of wide-band receiver systems on interferometer arrays enables one to undertake high-sensitivity and high-resolution radio continuum surveys of the Galactic plane in a reasonable amount of telescope time. However, to date, there are only a few such studies of the first quadrant of the Milky Way that have been carried out at frequencies below 1 GHz. The Giant Metrewave Radio Telescope (GMRT) has recently upgraded its receivers with wide-band capabilities (now called the uGMRT) and provides a good opportunity to conduct high resolution surveys, while also being sensitive to the extended structures. Aims. We wish to assess the feasibility of conducting a large-scale snapshot survey, the Metrewave Galactic Plane with the uGMRT Survey (MeGaPluG), to simultaneously map extended sources and compact objects at an angular resolution lower than $10''$ and a point source sensitivity of 0.15 mJy/beam. Methods. We performed an unbiased survey of a small portion of the Galactic plane, covering the W43/W44 regions ($l=29^\circ-35^\circ$ and $|b|<1^\circ$) in two frequency bands: 300$-$500 MHz and 550$-$750 MHz. The 200 MHz wide-band receivers on the uGMRT are employed to observe the target field in several pointings, spending nearly 14 minutes on each pointing in two separate scans. We developed an automated pipeline for the calibration, and a semi-automated self-calibration procedure is used to image each pointing using multi-scale CLEAN and outlier fields. Results. We produced continuum mosaics of the surveyed region at a final common resolution of $25''$ in the two bands that have central frequencies of 400 MHz and 650 MHz, with a point source sensitivity better than 5 mJy/beam. We plan to cover a larger footprint of the Galactic plane in the near future based on the lessons learnt from this study. (Abridged)

Abstract: Low-frequency gravitational wave experiments such as the Laser Interferometer Space Antenna and pulsar timing arrays are expected to detect individual massive black hole (MBH) binaries and mergers. However, secure methods of identifying the exact host galaxy of each MBH merger amongst the large number of galaxies in the gravitational wave localization region are currently lacking. We investigate the distinct morphological signatures of MBH merger host galaxies, using the Romulus25 cosmological simulation. We produce mock telescope images of 201 simulated galaxies in Romulus25 hosting recent MBH mergers, through stellar population synthesis and dust radiative transfer. Based on comparisons to mass- and redshift-matched control samples, we show that combining multiple morphological statistics via a linear discriminant analysis enables identification of the host galaxies of MBH mergers, with accuracies that increase with chirp mass and mass ratio. For mergers with high chirp masses (>10^8.2 Msun) and high mass ratios (>0.5), the accuracy of this approach reaches >80%, and does not decline for at least >1 Gyr after numerical merger. We argue that these trends arise because the most distinctive morphological characteristics of MBH merger and binary host galaxies are prominent classical bulges, rather than relatively short-lived morphological disturbances from their preceding galaxy mergers. Since these bulges are formed though major mergers of massive galaxies, they lead to (and become permanent signposts for) MBH binaries and mergers that have high chirp masses and mass ratios. Our results suggest that galaxy morphology can aid in identifying the host galaxies of future MBH binaries and mergers.

Abstract: The recent discovery of a 4 $\times$ 10$^7$ M$_{\odot}$ black hole (BH) in UHZ1 at $z =$ 10.3, just 450 Myr after the big bang, suggests that the seeds of the first quasars may have been direct-collapse black holes (DCBHs) from the collapse of supermassive primordial stars at $z \sim$ 20. This object was identified in James Webb Space Telescope (JWST) NIRcam and Chandra X-ray data, but recent studies suggest that radio emission from such a BH should also be visible to the Square Kilometer Array (SKA) and the next-generation Very Large Array (ngVLA). Here, we present estimates of radio flux for UHZ1 from 0.1 - 10 GHz, and find that SKA and ngVLA could detect it with integration times of 10 - 100 hr and just 1 - 10 hr, respectively. It may be possible to see this object with VLA now with longer integration times. The detection of radio emission from UHZ1 would be a first test of exciting new synergies between near infrared (NIR) and radio observatories that could open the era of $z \sim$ 5 - 15 quasar astronomy in the coming decade.

Abstract: We present an analysis of the degree of energy equipartition in a sample of 101 Monte Carlo numerical simulations of globular clusters (GCs) hosting either a system of stellar-mass black holes (BHS), an intermediate-mass black hole (IMBH) or neither of them. For the first time, we systematically explore the signatures that the presence of BHS or IMBHs produces on the degree of energy equipartition and if these signatures could be found in current observations. We show that a BHS can halt the evolution towards energy equipartition in the cluster centre. We also show that this effect grows stronger with the number of stellar-mass black holes in the GC. The signatures introduced by IMBHs depend on how dominant their masses are to the GCs and for how long the IMBH has co-evolved with its host GCs. IMBHs with a mass fraction below 2% of the cluster mass produce a similar dynamical effect to BHS, halting the energy equipartition evolution. IMBHs with a mass fraction larger than 2% can produce an inversion of the observed mass-dependency of the velocity dispersion, where the velocity dispersion grows with mass. We compare our results with observations of Galactic GCs and show that the observed range of the degree of energy equipartition in real clusters is consistent with that found in our analysis. In particular, we show that some Galactic GCs fall within the anomalous behaviour expected for systems hosting a BHS or an IMBH and are promising candidates for further dynamical analysis.

Abstract: We present photometric and morphological analyses of nuclear star clusters (NSCs) -- very dense, massive star clusters present in the central regions of most galaxies -- in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3. We fit the images in 2D to take into account the full complexity of the inner regions of these galaxies (including the contributions of nuclear disks and bars), isolating the nuclear star cluster and bulge components. We derive NSC radii and magnitudes in all 3 bands, which we then use to estimate NSC masses. Our sample significantly expands the sample of massive late-type galaxies with measured NSC properties. We clearly identify nuclear star clusters in nearly 80% of our galaxies, putting a lower limit on the nucleation fraction in these galaxies that is higher than previous estimates. We find that the NSCs in our massive disk galaxies are consistent with previous NSC mass-NSC radius and Galaxy Mass-NSC Mass relations. However, we also find a large spread in NSC masses, with a handful of galaxies hosting very low-mass, compact clusters. Our NSCs are aligned in PA with their host galaxy disks but are less flattened. They show no correlations with bar or bulge properties. Finally, we find the ratio of NSC to BH mass in our massive disk galaxy sample spans a factor of $\sim$300.