Galaxy formation and evolution

Abstract:

Abstract Stars in galactic centers are occasionally scattered so close to the central supermassive black hole that they are completely disrupted by tidal forces, initiating a transient accretion event. The aftermath of such a tidal disruption event (TDE) produces a bright-and-blue accretion flow which is known to persist for at least a decade (observationally) and can in principle produce ionizing radiation for hundreds of years. Tidal disruption events are known (observationally) to be overrepresented in galaxies which show extended emission line regions (EELRs), with no pre-TDE classical active galactic nucleus (AGN) activity, and to produce transient “coronal lines”, such as [FeX] and [FeXIV]. Using coupled CLOUDY-TDE disk simulations we show that tidal disruption event disks produce a sufficient ionizing radiation flux over their lifetimes to power both EELR of radial extents of r ∼ 104 light years, and coronal lines. EELRs are produced when the ionizing radiation interacts with low density nH ∼ 101 − 103 cm−3 clouds on galactic scales, while coronal lines are produced by high density nH ∼ 106 − 108 cm−3 clouds near the galactic center. High density gas in galactic centers will also result in the rapid switching on of narrow line features in post-TDE galaxies, and also various high-ionization lines which may be observed throughout the infrared with JWST. Galaxies with a higher intrinsic rate of tidal disruption events will be more likely to show macroscopic EELRs, which can be traced to originate from the previous tidal disruption event in that galaxy.

Abstract:

Abstract Using deep observations across three of the LOFAR Two-metre Sky Survey Deep Fields, this work measures the angular clustering of star forming galaxies (SFGs) and low-excitation radio galaxies (LERGs) to z ≲1.5 for faint sources, S144 MHz ≥200 μJy. We measure the angular auto-correlation of LOFAR sources in redshift bins and their cross-correlation with multi-wavelength sources to measure the evolving galaxy bias for SFGs and LERGs. Our work shows the bias of the radio-selected SFGs increases from $b=0.90^{+0.11}_{-0.10}$ at z ∼0.2 to $b=2.94^{+0.36}_{-0.36}$ at z ∼1.2; faster than the assumed b($z$)∝1/D($z$) models adopted in previous LOFAR cosmology studies (at sensitivities where AGN dominate), but in broad agreement with previous work. We further study the luminosity dependence of bias for SFGs and find little evidence for any luminosity dependence at fixed redshift, although uncertainties remain large for the sample sizes available. The LERG population instead shows a weaker redshift evolution with $b=2.33^{+0.28}_{-0.27}$ at z ∼0.7 to $b=2.65^{+0.57}_{-0.55}$ at z ∼1.2, though it is also consistent with the assumed bias evolution model (b($z$)∝1/D($z$)) within the measured uncertainties. For those LERGs which reside in quiescent galaxies (QLERGs), there is weak evidence that they are more biased than the general LERG population and evolve from b=$2.62^{+0.33}_{-0.33}$ at z ∼0.7 to $b=3.08^{+0.85}_{-0.84}$ at z ∼1.2. This suggests the halo environment of radio sources may be related to their properties. These measurements can help constrain models for the bias evolution of these source populations, and can help inform multi-tracer analyses.

Abstract:

Understanding the origin and evolution of supermassive black holes (SMBHs) stands as one of the most important challenges in astrophysics and cosmology, with little current theoretical consensus. Improved observational constraints on the cosmological evolution of SMBH demographics are needed. Here we report results of a search via photometric variability for SMBHs appearing as active galactic nuclei (AGN) in the cosmological volume defined by the Hubble Ultra Deep Field. This work includes particular focus on a new observation carried out in 2023 with the Hubble Space Telescope using the WFC3/IR/F140W, which is compared directly to equivalent data taken 11 yr earlier in 2012. Two earlier pairs of observations from 2009 to 2012 with WFC3/IR/F105W and WFC3/IR/F160W are also analyzed. We identify 521, 188, and 109 AGN candidates as nuclear sources that exhibit photometric variability at a level of 2σ, 2.5σ, and 3σ, respectively, in at least one filter. This sample includes 13, 3, and 2 AGN candidates at redshifts z > 6, when the Universe was ≲900 Myr old. After variability and luminosity function (down to MUV = −17 mag) completeness corrections, we estimate the comoving number density of SMBHs, nSMBH(z). At z ≳ 6, nSMBH ≳ 6 × 10−3 cMpc−3. At low z our observations are sensitive to AGN fainter than MUV = −17 mag, and we estimate nSMBH ≳ 10−2 cMpc−3. We discuss how these results place strong constraints on a variety of SMBH seeding theories.

Abstract:

We derive circular velocity curves (CVCs) from stellar dynamical models for ∼6000 nearby galaxies in the final data release of the Sloan Digital Sky Survey-IV MaNGA survey with integral-field spectroscopy, exploring connections between the inner gravitational potential (traced by CVC amplitude/shape) and galaxy properties. The maximum circular velocity ( Vcircmax ) and circular velocity at the half-light radius ( Vcirc(Remaj) ) both scale linearly with the stellar second velocity moment σe2≡〈V2+σ2〉 within the half-light isophote, following Vcircmax≈1.72σe (7% error) and Vcirc(Remaj)≈1.62σe (7% error). CVC shapes (rising, flat, declining) correlate strongly with structural and stellar population properties: declining curves dominate in massive, early-type, bulge-dominated galaxies with old, metal-rich stars and early quenching, while rising CVCs prevail in disk-dominated systems with younger stellar populations and ongoing star formation. Using a unified bulge–disk–halo model, we predict CVC shapes with minimal bias, identifying three governing parameters: bulge-to-total mass ratio (B/T), dark matter fraction within Re, and bulge Sérsic index. The distribution of CVC shapes across the mass–size plane reflects evolutionary pathways driven by (i) in situ star formation (spurring bulge growth) and (ii) dry mergers. This establishes CVC morphology as a diagnostic for galaxy evolution, linking dynamical signatures to structural and stellar population histories.