Astrophysics of Galaxies (astro-ph.GA)

The HASHTAG project II. Giant molecular cloud properties across the M31 disc

Sat, 01 Mar 2025 00:00:00 GMT

The HASHTAG project II. Giant molecular cloud properties across the M31 disc Deng, Yikai; Li, Zongnan; Li, Zhiyuan; Liu, Lijie; Ren, Zhiyuan; Athikkat-Eknath, Gayathri; de Grijs, Richard; Eales, Stephen A.; Eden, David J.; Iono, Daisuke; Jiao, Sihan; Lee, Bumhyun; Li, Di; Saintonge, Amelie; Smith, Matthew W. L.; Tang, Xindi; Tsai, Chaowei; van der Giessen, Stefan A.; Williams, Thomas G.; Wu, Jingwen We present a study of giant molecular cloud (GMC) properties in the Andromeda galaxy (M31) using CO(3-2) data from the James Clerk Maxwell Telescope (JCMT) in selected regions across the disc and in the nuclear ring, and comparing them with CO(1-0) observations from the IRAM 30m telescope in the same regions. We find that GMCs in the centre of M31 generally exhibit larger velocity dispersions (σ) and sizes (R) compared to those in the disc, while their average surface density (Σ) and turbulent pressure (P_turb) are lower. This low turbulent pressure in the central region is primarily due to the low density of molecular gas. The estimated GMC properties depend on the choice of CO transitions. Compared to CO(1-0), CO(3-2) exhibits smaller velocity dispersion and equivalent radius but higher surface density. These differences highlight the distinct physical conditions probed by different molecular gas tracers. We estimate the virial parameter α_vir∝σ²R/Σ and find that most molecular clouds exhibit high values (α_vir ~ 4 - 6) for both CO transitions, indicating that they are unbound. Furthermore, clouds in the nuclear ring display even larger α_vir values of ≲ 100, suggesting that they may be highly dynamic, short-lived structures, although they could potentially achieve equilibrium under the external pressure exerted by the surrounding interstellar medium.

PAMS: The Perseus Arm Molecular Survey-I. Survey description and first results

Sat, 01 Mar 2025 00:00:00 GMT

PAMS: The Perseus Arm Molecular Survey-I. Survey description and first results Rigby, Andrew J.; Thompson, Mark A.; Eden, David J.; Moore, Toby J. T.; Mutale, Mubela; Peretto, Nicolas; Plume, Rene; Urquhart, James S.; Williams, Gwenllian M.; Currie, Malcolm J. The external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in

$^{12}$

CO,

$^{13}$

CO, and C

$^{18}$

O (J = 3-2). With a survey area of

$\sim$

8 deg

$^2$

, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at

$\ell \approx 110^{\circ }$

and

$\ell \approx 135^{\circ }$

. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of

$T_\mathrm{mb}= 0.7$

-1.0 K in 0.3 km s

$^{-1}$

channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H

$_2$

column density from Herschel, we calculate representative values for the CO-to-H

$_2$

column-density X-factors, which are

$X_\mathrm{^{12}CO\, (3-2)}$

$\, =4.0\times 10^{20}$

and

$X_\mathrm{^{13}CO\, (3-2)}$

$\, =4.0\times 10^{21}$

$^{-2}$

(K km s

$^{-1}$

)

$^{-1}$

with a factor of 1.5 uncertainty. We find that the emission profiles, size-linewidth, and mass-radius relationships of

$^{13}$

CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the X-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.

Discovery of Metal-poor and Distant Pre–Main Sequence Candidates in WLM with JWST

Sat, 01 Feb 2025 00:00:00 GMT

Discovery of Metal-poor and Distant Pre–Main Sequence Candidates in WLM with JWST Kalari, Venu M.; Salinas, Ricardo; Andersen, Morten; De Marchi, Guido; Rubio, Monica; Vink, Jorick S.; Zinnecker, Hans We present the discovery of 12 metal-poor and distant pre–main sequence (PMS) candidates in the dwarf irregular galaxy Wolf–Lundmark–Melotte ∼968 kpc away, at a present-day metallicity of [Fe/H] ∼ –0.9. These candidates have masses between 1.25 and 5 M_⊙, with ages <10 Myr, and exhibit significant near-infrared excesses at 2.5 and 4.3 μm. They are concentrated within a cluster roughly 10 pc (2″) across, situated in the H II region [HM95]-9. These are the most distant and metal-poor PMS stars known, and they can offer new quantitative insights into star formation at low metallicities.

X-Shooting ULLYSES: Massive stars at low metallicity: X. Physical parameters and feedback of massive stars in the LMC N11 B star-forming region

Sat, 01 Mar 2025 00:00:00 GMT

X-Shooting ULLYSES: Massive stars at low metallicity: X. Physical parameters and feedback of massive stars in the LMC N11 B star-forming region Gómez-González, V. M. A.; Oskinova, L. M.; Hamann, W. -R.; Todt, H.; Pauli, D.; Reyero Serantes, S.; Bernini-Peron, M.; Sander, A. A. C.; Ramachandran, V.; Vink, J. S.; Crowther, P. A.; Berlanas, S. R.; ud-Doula, A.; Gormaz-Matamala, A. C.; Kehrig, C.; Kuiper, R.; Leitherer, C.; Mahy, L.; McLeod, A. F.; Mehner, A.; Morrell, N.; Shenar, T.; Telford, O. G.; van Loon, J. Th.; Tramper, F.; Wofford, A. Massive stars drive the ionization and mechanical feedback within young star-forming regions. The Large Magellanic Cloud (LMC) is an ideal galaxy for studying individual massive stars and quantifying their feedback contribution to the environment. We analyze eight exemplary targets in LMC N11 B from the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program using novel spectra from HST (COS and STIS) in the UV, and from VLT (X-shooter) in the optical. We model the spectra of early to late O-type stars using state-of-the-art PoWR atmosphere models. We determine the stellar and wind parameters (e.g., T_⋆, log g, L_⋆, Ṁ, and v_∞) of the analyzed objects, chemical abundances (C, N, and O), ionizing and mechanical feedback (Q_H, Q_HeI, Q_{He II}, and L_mec), and X-rays. We report ages of 2–4.5 Myr and masses of 30–60 M_⊙ for the analyzed stars in N11 B, which are consistent with a scenario of sequential star formation. We note that the observed wind-momentum–luminosity relation is consistent with theoretical predictions. We detect nitrogen enrichment by up to a factor of seven in most of the stars. However, we do not find a correlation between nitrogen enrichment and projected rotational velocity. Finally, based on their spectral type, we estimate the total ionizing photons injected from the O-type stars in N11 B into its environment. We report log (Σ Q_H) = 50.5 ph s^‑1, log (Σ Q_{He I}) = 49.6 ph s^‑1, and log (Σ Q_{He II})= 44.4 ph s^‑1, consistent with the total ionizing budget in N11.