分类： 天文学 >> 天文学 提交时间： 2023-02-19
Chong Ge
Ming Sun
Masafumi Yagi
Matteo Fossati
William Forman
Pavel Jáchym
Eugene Churazov
Irina Zhuravleva
Alessandro Boselli
Christine Jones
Li Ji
Rongxin Luo
摘要： Galaxy clusters grow primarily through the continuous accretion of group-scale haloes. Group galaxies experience preprocessing during their journey into clusters. A star-bursting compact group, the Blue Infalling Group (BIG), is plunging into the nearby cluster A1367. Previous optical observations reveal rich tidal features in the BIG members, and a long H$\alpha$ trail behind. Here we report the discovery of a projected $\sim 250$ kpc X-ray tail behind the BIG using Chandra and XMM-Newton observations. The total hot gas mass in the tail is $\sim 7\times 10^{10}\ {\rm M}_\odot$ with an X-ray bolometric luminosity of $\sim 3.8\times 10^{41}$ erg s$^{-1}$. The temperature along the tail is $\sim 1$ keV, but the apparent metallicity is very low, an indication of the multi-$T$ nature of the gas. The X-ray and H$\alpha$ surface brightnesses in the front part of the BIG tail follow the tight correlation established from a sample of stripped tails in nearby clusters, which suggests the multiphase gas originates from the mixing of the stripped interstellar medium (ISM) with the hot intracluster medium (ICM). Because thermal conduction and hydrodynamic instabilities are significantly suppressed, the stripped ISM can be long lived and produce ICM clumps. The BIG provides us a rare laboratory to study galaxy transformation and preprocessing.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jin Koda
Linda Watson
Francoise Combes
Monica Rubio
Samuel Boissier
Masafumi Yagi
David Thilker
Amanda M Lee
Yutaka Komiyama
Kana Morokuma-Matsui
Celia Verdugo
摘要： We report a CO(3-2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with ALMA. The observed 1kpc^2 region is at about 1.24 times the optical radius (R25) of the disk, where CO(2-1) was previously not detected. The detection and non-detection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A -- with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud and clump masses, estimated from CO(3-2), range from 8.2x10^2 to 2.3x10^4 Msun and from 2.7x10^2 to 7.5x10^3 Msun, respectively. The most massive clouds appear similar to Orion A in star formation activity as well as in mass, as expected if the cloud mass structure is universal. The overall low SF activity in the XUV disk could be due to the relative shortage of gas in the molecular phase. The clouds are distributed like chains up to 600 pc (or longer) in length, suggesting that the trigger of cloud formation is on large scales. The universal cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in the high-z universe. This study is the first demonstration that CO(3-2) is an efficient tracer of molecular clouds even in low-metallicity environments.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Chong Ge
Rongxin Luo
Ming Sun
Masafumi Yagi
Pavel Jáchym
Alessandro Boselli
Matteo Fossati
Paul E. J. Nulsen
Craig Sarazin
Tim Edge
Giuseppe Gavazzi
Massimo Gaspari
Jin Koda
Yutaka Komiyama
Michitoshi Yoshida
摘要： Recent studies have highlighted the potential significance of intracluster medium (ICM) clumping and its important implications for cluster cosmology and baryon physics. Many of the ICM clumps can originate from infalling galaxies, as stripped interstellar medium (ISM) mixing into the hot ICM. However, a direct connection between ICM clumping and stripped ISM has not been unambiguously established before. Here we present the discovery of the first and still the only known isolated cloud (or orphan cloud, OC) detected in both X-rays and H$\alpha$ in the nearby cluster Abell 1367. With an effective radius of 30 kpc, this cloud has an average X-ray temperature of 1.6 keV, a bolometric X-ray luminosity of $\sim 3.1\times 10^{41}$ erg s$^{-1}$ and a hot gas mass of $\sim 10^{10}\ {\rm M}_\odot$. From the MUSE data, the OC shows an interesting velocity gradient nearly along the east-west direction with a low level of velocity dispersion of $\sim 80$ km/s, which may suggest a low level of the ICM turbulence. The emission line diagnostics suggest little star formation in the main H$\alpha$ cloud and a LI(N)ER-like spectrum, but the excitation mechanism remain unclear. This example shows that the stripped ISM, even long time after the initial removal from the galaxy, can still induce the ICM inhomogeneities. We suggest that magnetic field can stabilize the OC by suppressing hydrodynamic instabilities and thermal conduction. This example also suggests that at least some ICM clumps are multi-phase in nature and implies that the ICM clumps can also be traced in H$\alpha$. Thus, future deep and wide-field H$\alpha$ survey can be used to probe the ICM clumping and turbulence.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ming Sun
Chong Ge
Rongxin Luo
Masafumi Yagi
Pavel Jáchym
Alessandro Boselli
Matteo Fossati
Paul E. J. Nulsen
Michitoshi Yoshida
Giuseppe Gavazzi
摘要： The impact of ram pressure stripping on galaxy evolution is well known. Recent multi-wavelength data have revealed many examples of galaxies undergoing stripping, often accompanied with multi-phase tails. As energy transfer in the multi-phase medium is an outstanding question in astrophysics, galaxies in stripping are great objects to study. Despite the recent burst of observational evidence, the relationship between gas in different phases in the tails is poorly known. Here we report a strong linear correlation between the X-ray surface brightness and the H$\alpha$ surface brightness of the diffuse gas in the stripped tails at $\sim$ 10 - 40 kpc scales, with a slope of $\sim$ 3.5. This discovery provides evidence for the mixing of the stripped interstellar medium with the hot intracluster medium as the origin of the multi-phase tails. The established relation in stripped tails, also in comparison with the likely related correlations in similar environments like galactic winds and X-ray cool cores, provides an important test for models of energy transfer in the multi-phase gas. It also indicates the importance of the H$\alpha$ data to study clumping and turbulence in the intracluster medium.
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