skip to main content


Title: ALPACA : a new semi-analytical model for metal absorption lines emerging from clumpy galactic environments
ABSTRACT

We present a new semi-analytical formalism for modelling metal absorption lines that emerge from a clumpy galactic environment, ALPACA. We predict the “down-the-barrel” (DTB) metal absorption line profiles and the equivalent width (EW) of absorption at different impact parameters (b) as a function of the clump properties, including clump kinematics, clump volume filling factor, clump number density profile, and clump ion column densities. With ALPACA, we jointly model the stacked DTB C ii λ1334 spectrum of a sample of z ∼ 3 Lyman break galaxies and the EW versus b profile of a sample of z ∼ 2 star-forming galaxy–galaxy pairs. ALPACA successfully reproduced two data sets simultaneously, and the best fit prefers a low clump volume filling factor (∼3 × 10−3). The radial velocities of the clumps are a superposition of a rapidly accelerated outflow with a maximum velocity of $\sim 400 \, {\mathrm{km}\, \mathrm{s}^{-1}}$ and a velocity dispersion of $\sigma \sim 120 \, {\mathrm{km}\, \mathrm{s}^{-1}}$. The joint modelling reveals a physical scenario where the absorption observed at a particular velocity is contributed by the clumps distributed over a fairly broad range of radii. We also find that the commonly adopted Sobolev approximation is at best only applicable within a narrow range of radii where the clumps are undergoing rapid acceleration in a non-volume-filling clumpy medium. Lastly, we find that the clump radial velocity profile may not be fully constrained by the joint modelling and spatially resolved Ly α emission modelling may help break the degeneracy.

 
more » « less
Award ID(s):
2009278
NSF-PAR ID:
10493480
Author(s) / Creator(s):
; ;
Publisher / Repository:
Oxford University Press
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
529
Issue:
1
ISSN:
0035-8711
Format(s):
Medium: X Size: p. 444-463
Size(s):
p. 444-463
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    ABSTRACT We present new observations of Lyman-α (Lyα) Blob 1 (LAB1) in the SSA22 protocluster region (z = 3.09) using the Keck Cosmic Web Imager and Keck Multi-object Spectrometer for Infrared Exploration. We have created a narrow-band Lyα image and identified several prominent features. By comparing the spatial distributions and intensities of Lyα and Hβ, we find that recombination of photo-ionized H i gas followed by resonant scattering is sufficient to explain all the observed Lyα/Hβ ratios. We further decode the spatially resolved Lyα profiles using both moment maps and radiative transfer modelling. By fitting a set of multiphase, ‘clumpy’ models to the observed Lyα profiles, we manage to reasonably constrain many parameters, namely the H i number density in the interclump medium (ICM), the cloud volume filling factor, the random velocity and outflow velocity of the clumps, the H i outflow velocity of the ICM, and the local systemic redshift. Our model has successfully reproduced the diverse Lyα morphologies, and the main results are: (1) the observed Lyα spectra require relatively few clumps per line of sight as they have significant fluxes at the line centre; (2) the velocity dispersion of the clumps yields a significant broadening of the spectra as observed; (3) the clump bulk outflow can also cause additional broadening if the H i in the ICM is optically thick; (4) and the H i in the ICM is responsible for the absorption feature close to the Lyα line centre. 
    more » « less
  2. ABSTRACT We present Atacama Large Millimetre/submillimetre Array observations of the brightest cluster galaxy Hydra-A, a nearby (z = 0.054) giant elliptical galaxy with powerful and extended radio jets. The observations reveal CO(1−0), CO(2–1), 13CO(2–1), CN(2–1), SiO(5–4), HCO+(1–0), HCO+(2–1), HCN(1–0), HCN(2–1), HNC(1–0), and H2CO(3–2) absorption lines against the galaxy’s bright and compact active galactic nucleus. These absorption features are due to at least 12 individual molecular clouds that lie close to the centre of the galaxy and have velocities of approximately −50 to +10 km s−1 relative to its recession velocity, where positive values correspond to inward motion. The absorption profiles are evidence of a clumpy interstellar medium within brightest cluster galaxies composed of clouds with similar column densities, velocity dispersions, and excitation temperatures to those found at radii of several kpc in the Milky Way. We also show potential variation in a ∼10 km s−1 wide section of the absorption profile over a 2 yr time-scale, most likely caused by relativistic motions in the hot spots of the continuum source that change the background illumination of the absorbing clouds. 
    more » « less
  3. null (Ed.)
    ABSTRACT We investigate the redshift evolution of the intrinsic alignments (IAs) of galaxies in the MassiveBlackII (MBII) simulation. We select galaxy samples above fixed subhalo mass cuts ($M_h\gt 10^{11,12,13}\,\mathrm{M}_{\odot }\, h^{-1}$) at z = 0.6 and trace their progenitors to z = 3 along their merger trees. Dark matter components of z = 0.6 galaxies are more spherical than their progenitors while stellar matter components tend to be less spherical than their progenitors. The distribution of the galaxy–subhalo misalignment angle peaks at ∼10 deg with a mild increase with time. The evolution of the ellipticity–direction (ED) correlation amplitude ω(r) of galaxies (which quantifies the tendency of galaxies to preferentially point towards surrounding matter overdensities) is governed by the evolution in the alignment of underlying dark matter (DM) subhaloes to the matter density of field, as well as the alignment between galaxies and their DM subhaloes. At scales $\sim 1~\mathrm{Mpc}\, h^{-1}$, the alignment between DM subhaloes and matter overdensity gets suppressed with time, whereas the alignment between galaxies and DM subhaloes is enhanced. These competing tendencies lead to a complex redshift evolution of ω(r) for galaxies at $\sim 1~\mathrm{Mpc}\, h^{-1}$. At scales $\gt 1~\mathrm{Mpc}\, h^{-1}$, alignment between DM subhaloes and matter overdensity does not evolve significantly; the evolution of the galaxy–subhalo misalignment therefore leads to an increase in ω(r) for galaxies by a factor of ∼4 from z = 3 to 0.6 at scales $\gt 1~\mathrm{Mpc}\, h^{-1}$. The balance between competing physical effects is scale dependent, leading to different conclusions at much smaller scales ($\sim 0.1~\mathrm{Mpc}\, h^{-1}$). 
    more » « less
  4. Abstract

    Massive, star-forming clumps are a common feature of high-redshift star-forming galaxies. How they formed, and why they are so rare at low redshift, remains unclear. In this paper we identify the largest sample yet of clumpy galaxies (7050) at low redshift using data from the citizen science project Galaxy Zoo: Clump Scout, in which volunteers classified 58,550 Sloan Digital Sky Survey (SDSS) galaxies spanning redshift 0.02 <z< 0.15. We apply a robust completeness correction by comparing with simulated clumps identified by the same method. Requiring that the ratio of clump to galaxy flux in the SDSSuband be greater than 8% (similar to clump definitions used by other works), we estimate the fraction of local star-forming galaxies hosting at least one clump (fclumpy) to be3.220.34+0.38%. We also compute the same fraction with a less stringent relative flux cut of 3% (12.680.88+1.38%), as the higher number count and lower statistical noise of this fraction permit finer comparison with future low-redshift clumpy galaxy studies. Our results reveal a sharp decline infclumpyover 0 <z< 0.5. The minor merger rate remains roughly constant over the same span, so we suggest that minor mergers are unlikely to be the primary driver of clump formation. Instead, the rate of galaxy turbulence is a better tracer forfclumpyover 0 <z< 1.5 for galaxies of all masses, which supports the idea that clump formation is primarily driven by violent disk instability for all galaxy populations during this period.

     
    more » « less
  5. ABSTRACT

    While the first “seeds” of supermassive black holes (BH) can range from $\sim 10^2-10^6 \rm ~{\rm M}_{\odot }$, the lowest mass seeds ($\lesssim 10^3~\rm {\rm M}_{\odot }$) are inaccessible to most cosmological simulations due to resolution limitations. We present our new BRAHMA simulations that use a novel flexible seeding approach to predict the $z\ge 7$ BH populations for low-mass seeds. We ran two types of boxes that model $\sim 10^3~\rm {\rm M}_{\odot }$ seeds using two distinct but mutually consistent seeding prescriptions at different simulation resolutions. First, we have the highest resolution $[9~\mathrm{Mpc}]^3$ (BRAHMA-9-D3) boxes that directly resolve $\sim 10^3~\rm {\rm M}_{\odot }$ seeds and place them within haloes with dense, metal-poor gas. Second, we have lower resolution, larger volume $[18~\mathrm{Mpc}]^3$ (BRAHMA-18-E4), and $\sim [36~\mathrm{Mpc}]^3$ (BRAHMA-36-E5) boxes that seed their smallest resolvable $\sim 10^4~\&~10^5~\mathrm{{\rm M}_{\odot }}$ BH descendants using new stochastic seeding prescriptions calibrated using BRAHMA-9-D3. The three boxes together probe key BH observables between $\sim 10^3\,\mathrm{ and}\,10^7~\rm {\rm M}_{\odot }$. The active galactic nuclei (AGN) luminosity function variations are small (factors of $\sim 2-3$) at the anticipated detection limits of potential future X-ray facilities ($\sim 10^{43}~ \mathrm{ergs~s^{-1}}$ at $z\sim 7$). Our simulations predict BHs $\sim 10-100$ times heavier than the local $M_*$ versus $M_{\mathrm{ bh}}$ relations, consistent with several JWST-detected AGN. For different seed models, our simulations merge binaries at $\sim 1-15~\mathrm{kpc}$, with rates of $\sim 200-2000$ yr−1 for $\gtrsim 10^3~\rm {\rm M}_{\odot }$ BHs, $\sim 6-60$ yr−1 for $\gtrsim 10^4~\rm {\rm M}_{\odot }$ BHs, and up to $\sim 10$ yr−1 amongst $\gtrsim 10^5~\rm {\rm M}_{\odot }$ BHs. These results suggest that Laser Interferometer Space Antenna mission has promising prospects for constraining seed models.

     
    more » « less