分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Previous studies have shown significant differences in the enhancement of the star-formation rate (SFR) and the star-formation efficiency (SFE=SFR/M_mol) between spiral-spiral and spiral-elliptical mergers. In order to shed light on the physical mechanism of these differences, we present NOEMA observations of the molecular gas distribution and kinematics (linear resolutions of ~ 2kpc) in two representative close major-merger star-forming pairs: the spiral-elliptical pair Arp142 and the spiral-spiral pair Arp238. The CO in Arp142 is widely distributed over a highly distorted disk without any nuclear concentration, and an off-centric ring-like structure is discovered in channel maps. The SFE varies significantly within Arp142, with a starburst region (Region 1) near the eastern tip of the distorted disk showing an SFE ~0.3 dex above the mean of the control sample of isolated galaxies, and the SFE of the main disk (Region 4) 0.43 dex lower than the mean of the control sample. In contrast, the CO emission in Arp238 is detected only in two compact sources at the galactic centers. Compared to the control sample, Arp238-E shows an SFE enhancement of more than 1 dex whereas Arp238-W has an enhancement of ~0.7 dex. We suggest that the extended CO distribution and the large SFE variation in Arp142 are due to an expanding large-scale ring triggered by a recent high-speed head-on collision between the spiral galaxy and the elliptical galaxy, and the compact CO sources with high SFEs in Arp238 are associated with nuclear starbursts induced by gravitational tidal torques in a low-speed coplanar interaction.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Giulia Pagnini
Paola Di Matteo
Sergey Khoperskov
Alessandra Mastrobuono-Battisti
Misha Haywood
Florent Renaud
Françoise Combes
摘要： Reconstructing how all the stellar components of the Galaxy formed and assembled over time, by studying the properties of the stars which make it, is the aim of Galactic archeology. In these last years, thanks to the launch of the ESA Gaia astrometric mission, and the development of many spectroscopic surveys, we are for the first time in the position to delve into the layers of the past of our galaxy. Globular clusters (GCs) play a fundamental role in this research field since they are among the oldest stellar systems in the Milky Way (MW) and so bear witness of its entire past. In the recent years, there have been several attempts to constrain the nature of clusters (accreted or formed in the MW itself) through the analysis of kinematic spaces and to reconstruct from this the properties of the accretions events experienced by the MW through time. This work aims to test a widely-used assumption about the clustering of the accreted populations of GCs in the integrals of motions space. We analyze a set of dissipation-less N-body simulations that reproduce the accretion of one or two satellites with their GC population on a MW-type galaxy. Our results demonstrate that a significant overlap between accreted and "kinematically-heated" in-situ GCs is expected in kinematic spaces, for mergers with mass ratios of 1:10. In contrast with standard assumptions made in the literature so far, we find that accreted GCs do not show dynamical coherence, that is they do not cluster in kinematic spaces. In addition, GCs can also be found in regions dominated by stars which have a different origin (i.e. different progenitor). This casts doubt on the association between GCs and field stars that is generally made in the literature to assign them to a common origin. Our findings severely question the recovered accretion history of the MW based on the phase-space clustering of the GC population.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Eva Schinnerer
Eric Emsellem
Jonathan D. Henshaw
Daizhong Liu
Sharon E. Meidt
Miguel Querejeta
Florent Renaud
Mattia C. Sormani
Jiayi Sun
Oleg V. Egorov
Kirsten L. Larson
Adam K. Leroy
Erik Rosolowsky
Karin M. Sandstrom
T. G. Williams
Ashley T. Barnes
F. Bigiel
Melanie Chevance
Yixian Cao
Rupali Chandar
摘要： Large-scale bars can fuel galaxy centers with molecular gas, often leading to the development of dense ring-like structures where intense star formation occurs, forming a very different environment compared to galactic disks. We pair ~0.3" (30pc) resolution new JWST/MIRI imaging with archival ALMA CO(2-1) mapping of the central ~5kpc of the nearby barred spiral galaxy NGC1365, to investigate the physical mechanisms responsible for this extreme star formation. The molecular gas morphology is resolved into two well-known bright bar lanes that surround a smooth dynamically cold gas disk (R_gal ~ 475pc) reminiscent of non-star-forming disks in early type galaxies and likely fed by gas inflow triggered by stellar feedback in the lanes. The lanes host a large number of JWST-identified massive young star clusters. We find some evidence for temporal star formation evolution along the ring. The complex kinematics in the gas lanes reveal strong streaming motions and may be consistent with convergence of gas streamlines expected there. Indeed, the extreme line-widths are found to be the result of inter-`cloud' motion between gas peaks; ScousePy decomposition reveals multiple components with line widths of ~ 19km/s and surface densities of ~ 800M_sun/pc^2, similar to the properties observed throughout the rest of the central molecular gas structure. Tailored hydro-dynamical simulations exhibit many of the observed properties and imply that the observed structures are transient and highly time-variable. From our study of NGC1365, we conclude that it is predominantly the high gas inflow triggered by the bar that is setting the star formation in its CMZ.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ashley T. Barnes
Elizabeth J. Watkins
Sharon E. Meidt
Kathryn Kreckel
Mattia C. Sormani
Robin G. Tress
Simon C. O. Glover
Frank Bigiel
Rupali Chandar
Eric Emsellem
Janice C. Lee
Adam K. Leroy
Karin M. Sandstrom
Eva Schinnerer
Erik W. Rosolowsky
Francesco Belfiore
Guillermo Blanc
Mederic Boquien
Jakob S. den Brok
Yixian Cao
摘要： We present a high-resolution view of bubbles within The Phantom Galaxy (NGC 628); a nearby (~10Mpc), star-forming (~2Msun/yr), face-on (i~9deg) grand-design spiral galaxy. With new data obtained as part of the PHANGS-JWST treasury program, we perform a detailed case-study of two regions of interest, one of which contains the largest and most prominent bubble in the galaxy (The Phantom Void; over 1kpc in diameter), and the other being a smaller region that may be the precursor to such a large bubble (The Precursor Phantom Void). When comparing to matched resolution Halpha observations from the Hubble Space Telescope (HST), we see that the ionized gas is brightest in the shells of both bubbles, and is coincident with the youngest (~1Myr) and most massive (~100,000Msun) stellar associations. We also find an older generation (~20Myr) of stellar associations is present within the bubble of The Phantom Void. From our kinematic analysis of the HI, H2 (CO) and HII gas across The Phantom Void, we infer a high expansion speed of around 15 to 50km/s. The large size and high expansion speed of The Phantom Void suggest that the driving mechanism is sustained stellar feedback due to multiple mechanisms, where early feedback first cleared a bubble (as we observe now in The Precursor Phantom Void), and since then SNe have been exploding within the cavity, and have accelerated the shell. Finally, comparison to simulations shows a striking resemblance to our JWST observations, and suggests that such large-scale stellar feedback-driven bubbles should be common within other galaxies.
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