arXiv subjects

Xuepeng Chen

Publications and source records attributed to Xuepeng Chen.

At least 55 records · Page 3Linked to original sources

arXiv2023

On the Spatial Distribution of $^{13}$CO Structures within $^{12}$CO Molecular Clouds

We look into the 2851 $^{12}$CO molecular clouds harboring $^{13}$CO structures to reveal the distribution of the projected angular separations and radial velocity separations between their internal $^{13}$CO structures. The projected angular separations are determined using the minimal spanning tree algorithm. We find that $\sim$ 50$\%$ of the angular separations fall in a narrow range of $\sim$ 3 - 7 arcmin with a median of $\sim$ 5 arcmin, and the corresponding radial velocity separations mainly range from $\sim$ 0.3 km s$^{-1}$ to 2.5 km s$^{-1}$. The mean and standard deviation of the angular separations of the internal $^{13}$CO structures within $^{12}$CO clouds appear to be universal, independent of the $^{12}$CO cloud angular areas and the counts of their internal $^{13}$CO structures. We also reveal a scaling relation between the $^{12}$CO cloud angular area and its harbored $^{13}$CO structure count. These results suggest there is a preferred angular separation between $^{13}$CO structures in these $^{12}$CO clouds, considering the distance effects. According to that, we propose an alternative picture for the assembly and destruction of molecular clouds: there is a fundamental separation for the internal structures of molecular clouds, the build-up and destruction of molecular clouds proceeds under this fundamental unit.

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arXiv2022

The Cassiopeia Filament: A Blown Spur of the Local Arm

We present wide-field and high-sensitivity CO(1-0) molecular line observations toward the Cassiopeia region, using the 13.7m millimeter telescope of the Purple Mountain Observatory (PMO). The CO observations reveal a large-scale highly filamentary molecular cloud within the Galactic region of 132\fdg0\,$\geq$\,$l$\,$\geq$\,122\fdg0 and -1\fdg0\,$\leq$\,$b$\,$\leq$\,3\fdg0 and the velocity range from approximately +1 to +4 km/s. The measured length of the large-scale filament, referred to as the Cassiopeia Filament, is about 390 pc. The observed properties of the Cassiopeia Filament, such as length, column density, and velocity gradient, are consistent with those synthetic large-scale filaments in the inter-arm regions. Based on its observed properties and location on the Galactic plane, we suggest that the Cassiopeia Filament is a spur of the Local arm, which is formed due to the galactic shear. The western end of the Cassiopeia Filament shows a giant arc-like molecular gas shell, which is extending in the velocity range from roughly -1 to +7 km/s. Finger-like structures, with systematic velocity gradients, are detected in the shell. The CO kinematics suggest that the large shell is expanding at a velocity of ~6.5 km/s. Both the shell and finger-like structures outline a giant bubble with a radius of ~16 pc, which is likely produced by stellar wind from the progenitor star of a supernova remnant. The observed spectral linewidths suggest that the whole Cassiopeia Filament was quiescent initially until its west part was blown by stellar wind and became supersonically turbulent.

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arXiv2022

CO(J = 1-0) Observations toward the Filamentary Cloud in the Galactic Region of $153.60^{\circ} \leqslant l \leqslant 156.50^{\circ}$ and $1.85^{\circ} \leqslant b \leqslant 3.50^{\circ}$

We present observations of $J$=1-0 transition lines of ${ }^{12} \mathrm{CO}$, ${ }^{13} \mathrm{CO}$, and $\mathrm{C}^{18} \mathrm{O}$ towards the Galactic region of $153.60^{\circ} \leqslant l \leqslant 156.50^{\circ}$ and $1.85^{\circ} \leqslant b \leqslant 3.50^{\circ}$, using the Purple Mountain Observatory (PMO) 13.7 m millimeter telescope. Based on the \tht data, one main filament and five sub-filaments are found together as a network structure in the velocity interval of $[-42.5, -30.0] \,\mathrm{km} \mathrm{\,s}^{-1}$. The kinematic distance of this molecular cloud (MC) is estimated to be $\sim4.5 \mathrm{\,kpc}$. The median length, width, excitation temperature, line mass of these filaments are $\sim49 \mathrm{\,pc}$, $\sim2.9 \mathrm{\,pc}$, $\sim8.9 \mathrm{\,K}$, and $\sim39 \,M_{\odot} \mathrm{pc}^{-1}$, respectively. The velocity structures along these filaments exhibit oscillatory patterns, which are likely caused by the fragmentation or accretion process along these filaments. The maximum accretion rate is estimated to be as high as $\sim700 \,M_{\odot} \mathrm{pc}^{-1}$. A total of $\sim162$ \tht clumps and $\sim 103$ young stellar objects (YSOs) are identified in this region. Most of the clumps are in gravitationally bound states. Three \hii regions (G154.359+2.606, SH2-211, SH2-212) are found to be located in the apexes of the filaments. Intense star forming activities are found along the entire filamentary cloud. The observed results may help us to better understand the link between filaments and massive star formation.

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arXiv2022

CO Emission Delineating the Interface between the Milky Way Nuclear Wind Cavity and the Gaseous Disk

Based on the MWISP survey, we study high-z CO emission toward the tangent points, in which the distances of the molecular clouds (MCs) are well determined. In the region of l=12-26 deg and |b|<5.1 deg, a total of 321 MCs with |z|> 110 pc are identified, of which nearly 30 extreme high-z MCs (EHMCs at |z|> 260 pc) are concentrated in a narrow region of R_GC=2.6-3.1 kpc. The EHMC concentrations, together with other high-z MCs at R_GC=2.3-2.6 kpc, constitute molecular crater-wall structures surrounding the edges of the HI voids that are physically associated with the Fermi bubbles. Intriguingly, some large high-z MCs, which lie in the crater walls above and below the Galactic plane, show cometary structures with the head toward the plane, favouring the scenario that the entrained molecular gas moves with the multi-phase flows from the plane to the high-z regions. We suggest that the Milky Way nuclear wind has a significant impact on the Galactic gaseous disk. The powerful nuclear wind at ~3-6 Myr ago is likely responsible for the observational features, (1) the enhanced CO gas lying in the edges of the HI voids, (2) the deficiency of atomic and molecular gas within R_GC<3 kpc, (3) the possible connection between the EHMC concentrations and the 3-kpc arm, and (4) the elongated high-z MCs with the tail pointing away from the Galactic plane.

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arXiv2021

Feedback from $γ$~Cassiopeiae: Large Expanding Cavity, Accelerating Cometary Globules, and Peculiar X-ray Emission

We present wide-field multi-wavelength observations of $γ$ Cassiopeiae (or $γ$~Cas for short) in order to study its feedback toward the interstellar environment. A large expanding cavity is discovered toward $γ$~Cas in the neutral hydrogen (HI) images at a systemic velocity of about -10 km/s. The measured dimension of the cavity is roughly 2.0 deg $\times$ 1.4 deg (or 6.0 pc $\times$ 4.2 pc at a distance of 168 pc), while the expansion velocity is about 5.0$\pm$0.5 km/s. The CO observations reveal systematic velocity gradients in IC63 (about 20 km/s/pc) and IC59 (about 30 km/s/pc), two cometary globules illuminated by $γ$~Cas, proving fast acceleration of the globules under stellar radiation pressure. The gas kinematics indicate that the cavity is opened by strong stellar wind, which has high potential to lead to the peculiar X-ray emission observed in $γ$~Cas. Our result favors a recent new scenario that emphasizes the roles of stellar wind and binarity in the X-ray emission of the $γ$~Cas stars.

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arXiv2021

M17 MIR: A massive protostar with multiple accretion Outbursts

We report the discovery of a massive protostar M17~MIR embedded in a hot molecular core in M17. The multiwavelength data obtained during 1993--2019 show significant mid-IR (MIR) variations, which can be split into three stages: the decreasing phase during 1993.03--mid-2004, the quiescent phase from mid-2004 to mid-2010, and the rebrightening phase from mid-2010 until now. The variation of the 22\,GHz H$_2$O maser emission, together with the MIR variation, indicates an enhanced disk accretion rate onto M17~MIR during the decreasing and rebrightening phases. Radiative transfer modeling of the spectral energy distributions of M17~MIR in the 2005 epoch (quiescent) and 2017 epoch (accretion outburst) constrains the basic stellar parameters of M17~MIR, which is an intermediate-mass protostar (M~5.4 Msun) with accretion rate ~1.1x10^-5 Msun in the 2005 epoch and ~1.7x10^-3 Msun/yr in the 2017 epoch. The enhanced accretion rate during outburst induces the luminosity outburst $ΔL\approx7600 $Lsun. In the accretion outburst, a larger stellar radius is required to produce accretion rate consistent with the value estimated from the kinematics of water masers. M17 MIR shows two accretion outbursts ($Δt\sim 9-20$ yr) with outburst magnitudes of 2 mag, separated by a 6 yr quiescent phase. The accretion outbusrt occupies 83\% of the time over 26 yr. The accretion rate in outburst is variable with amplitude much lower than the contrast between quiescent and outburst phases. The extreme youth of M17 MIR suggests that minor accretion bursts are frequent in the earliest stages of massive star formation.

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arXiv2021

A wide-field CO survey towards the California Molecular Filament

We present the survey of $^{12}$CO/$^{13}$CO/C$^{18}$O (J=1-0) toward the California Molecular Cloud (CMC) within the region of 161.75$^{\circ} \leqslant l \leqslant$ 167.75$^{\circ}$,-9.5$^{\circ} \leqslant b \leqslant $-7.5$^{\circ}$, using the Purple Mountain Observatory (PMO) 13.7 m millimeter telescope. Adopting a distance of 470 pc, the mass of the observed molecular cloud estimated from $^{12}$CO, $^{13}$CO, and C$^{18}$O is about 2.59$\times$10$^{4}$ M$_\odot$, 0.85$\times$10$^{4}$ M$_\odot$, and 0.09$\times$10$^{4}$ M$_\odot$, respectively. A large-scale continuous filament extending about 72 pc is revealed from the $^{13}$CO images. A systematic velocity gradient perpendicular to the major axis appears and is measured to be $\sim$ 0.82 km s$^{-1}$ pc$^{-1}$. The kinematics along the filament shows an oscillation pattern with a fragmentation wavelength of $\sim$ 2.3 pc and velocity amplitude of $\sim$ 0.92 km s$^{-1}$, which may be related with core-forming flows. Furthermore, assuming an inclination angle to the plane of the sky of 45$^{\circ}$, the estimated average accretion rate is $\sim$ 101 M$_\odot$ Myr$^{-1}$ for the cluster LkH$α$ 101 and $\sim$ 21 M$_\odot$ Myr$^{-1}$ for the other regions. In the C$^{18}$O observations, the large-scale filament could be resolved into multiple substructures and their dynamics are consistent with the scenario of filament formation from converging flows. Approximately 225 C$^{18}$O cores are extracted, of which 181 are starless cores. Roughly 37$\%$ (67/181) of the starless cores have $α_{\text{vir}}$ less than 1. Twenty outflow candidates are identified along the filament. Our results indicate active early-phase star formation along the large-scale filament in the CMC region.

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arXiv2021

Examinations of CO completeness based on three independent CO surveys

We report the global properties recovered by an ongoing CO survey of the Milky Way Imaging Scroll Painting (MWISP) toward the Galactic outskirts. %To better understand the observational biases, Our results are also compared to those extracted by a uniform decomposition method from the CfA 1.2 m CO survey and the FCRAO 14 m outer Galaxy survey (OGS). We find that more extended and unseen structures are present in the MWISP data. The total flux across the disk recovered by the MWISP survey is 1.6 times larger than those recovered by the CfA and OGS surveys in the case of the same resolution. The discrepancies are scaling with distance. For example, in the outermost OSC arm, the flux ratios for MWISP-to-CfA and MWISP-to-OGS increase up to 43.8 and 7.4, respectively. Nonetheless, the census of molecular gas in our Galaxy is still far from complete by the MWISP, with flux completeness of $<$58%. The total mass ratios of the tabulated molecular clouds between different surveys are similar to the CO flux ratio. The application of these ratios to the total H$_{\rm 2}$ mass of our Galaxy yields a correction factor of at least 1.4, meaning that the H$_{\rm 2}$ mass of our Galaxy should be at least 40% more massive than previously determined. Including the completeness correction, an even more significant fraction of the matter should be contributed by baryonic matter. The mass spectrum in the outer Galactic plane is better described by a non-truncating power-law with $γ$=$-$1.83$\pm$0.05, and an upper mass of $M_0$=(1.3$\pm$0.5)$\times$10$^{\rm 6}$ $M_\odot$.

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arXiv2021

Molecular gas distribution perpendicular to the Galactic plane

We use the ~370 square degrees data from the MWISP CO survey to study the vertical distribution of the molecular clouds (MCs) toward the tangent points in the region of l=[16,52]deg and |b|<5.1deg. The molecular disk consists of two components with the layer thickness (FWHM) of ~85pc and ~280pc, respectively. In the inner Galaxy, the molecular mass in the thin disk is dominant, while the molecular mass traced by the discrete MCs with weak CO emission in the thick disk is probably <10% of the whole molecular disk. For the CO gas in the thick disk, we identified 1055 high-z MCs that are >100pc from the Galactic plane. However, only a few samples (i.e., 32 MCs) are located in the |z|>360pc region. Typically, the discrete MCs of the thick disk population have a median peak temperature of 2.1 K, a median velocity dispersion of 0.8km/s, and a median effective radius of 2.5pc. The median surface density of these MCs is 6.8 Msun/pc^2, indicating very faint CO emission for these high-z MCs. The cloud-cloud velocity dispersion is 4.9+-1.3 km/s and a linear variation with a slope of -0.4 km/s/kpc is obtained in the region of R_GC=2.2-6.4kpc. Assuming that these clouds are supported by their turbulent motions against the gravitational pull of the disk, a model of rho0(R) = 1.28exp(-R/3.2kpc) Msun/pc^3 can be used to describe the distribution of the total mass density in the Galactic midplane.

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arXiv2020

Detection of a Disk Surrounding the Variably Accreting Young Star HBC722

We present new ALMA 233 GHz continuum observations of the FU Orionis Object HBC722. With these data we detect HBC722 at millimeter wavelengths for the first time, use this detection to calculate a circumstellar disk mass of 0.024 solar masses, and discuss implications for the burst triggering mechanism.

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arXiv2020

Molecular Clouds Surrounding Supernova Remnant G43.9+1.6: Associated and Non-associated

Many supernova remnants (SNRs) are considered to evolve in molecular environments, but the associations between SNRs and molecular clouds (MCs) are often unclear. Being aware of such ambiguous case, we report our study on the molecular environment towards the SNR G43.9+1.6 by CO line observations. We investigated the correlations between the SNR and MCs at different velocities, and found two velocity components, i.e. $\sim$5 km s$^{-1}$ and $\sim$50 km s$^{-1}$ velocity components, showing spatial correlations with the remnant. However, no dynamical evidence of disturbance was found for the $\sim$5 km s$^{-1}$ velocity component. At the distance of the $\sim$5 km s$^{-1}$ velocity component, either near or far distance, the derived physical parameters are unreasonable too. We conclude that the SNR is not associated with the $\sim$5 km s$^{-1}$ velocity component, and their spatial correlation is just a chance correlation. For the $\sim$50 km s$^{-1}$ velocity component, dynamical evidence of disturbances, as well as the spatial correlation, indicate that it is associated with the SNR. We found that all the CO spectra extracted from the molecular clumps distributed along the border of the remnant are with broadened components presented, which can be fitted by Gaussian functions. By further analysis, we suggest that the SNR is at a near kinematic distance of about 3.1 kpc.

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arXiv2020

Local Molecular Gas toward the Aquila Rift Region

We present the results of a ~250 square degrees CO mapping (+26d 4.1x10^5 Msun in the whole region. In fact, the mass of the molecular gas is dominated by the W40 giant molecular cloud (GMC) at ~474 pc (~1.4x10^5 Msun) and the GMC complex G036.0+01.0 at ~560-670 pc (~2.0x10^5 Msun), while the MCs at ~220-260pc have gas masses of 10^2-10^3 Msun. Interestingly, an ~80pc long filamentary MC G044.0-02.5 at a distance of ~404 pc shows a systematic velocity gradient along and perpendicular to the major axis of the filament. The HI gas with the enhanced emission has the similar spatial morphologies and velocity features compared to the corresponding CO structure, indicating that the large-scale converging HI flows are probably responsible for the formation of the MC. Meanwhile, the long filamentary MC consists of many sub-filaments with the lengths ranging from ~0.5 pc to several pc, as well as prevalent networks of filaments in other large-scale local MCs.

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arXiv2020

Searching for Molecular Outflows with Support Vector Machines: Dark Cloud Complex in Cygnus

We present a survey of molecular outflows across the dark cloud complex in the Cygnus region, based on 46.75 deg^2 field of CO isotopologues data from Milky Way Imaging Scroll Painting (MWISP) survey. A supervised machine learning algorithm, Support Vector Machine (SVM), is introduced to accelerate our visual assessment of outflow features in the data cube of 12CO and 13CO J = 1-0 emission. A total of 130 outflow candidates are identified, of which 77 show bipolar structures and 118 are new detections. Spatially, these outflows are located inside dense molecular clouds and some of them are found in clusters or in elongated linear structures tracing the underlying gas filament morphology. Along the line of sight, 97, 31, and 2 candidates reside in the Local, Perseus, and Outer arm, respectively. Young stellar objects as outflow drivers are found near most outflows, while 36 candidates show no associated source. The clusters of outflows that we detect are inhomogeneous in their properties; nevertheless, we show that the outflows cannot inject turbulent energy on cloud scales. Instead, at best, they are restricted to affecting the so called "clump" and "core" scales, and this only on short (~0.3 Myr) estimated timescales. Combined with outflow samples in the literature, our work shows a tight outflow mass-size correlation.

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arXiv2019

CO~($J=1-0$) Observations toward Filamentary Molecular Clouds in the Galactic Region with $l = [169\arcdeg.75, 174\arcdeg.75], b = [-0\arcdeg.75, 0\arcdeg.5]$

We present observations of the CO isotopologues ($^{12}$CO, $^{13}$CO, and C$^{18}$O) toward the Galactic region with $169\arcdeg.75 \leqslant l \leqslant 174\arcdeg.75$ and $-0\arcdeg.75 \leqslant b \leqslant 0\arcdeg.5$, using the Purple Mountain Observatory 13.7~m millimeter-wavelength telescope. Based on the $^{13}$CO~($J = 1-0$) data, we find five molecular clouds within the velocity range between $-$25 and 8~km~s$^{-1}$ that are all characterized by conspicuous filamentary structures. We have identified eight filaments with a length of 6.38--28.45~pc, a mean H$_2$ column density of 0.70$\times$10$^{21}$--6.53$\times$10$^{21}$~cm$^{-2}$, and a line mass of 20.24--161.91~$M_\sun$ pc$^{-1}$, assuming a distance of $\sim$1.7~kpc. Gaussian fittings to the inner parts of the radial density profiles lead to a mean FWHM width of 1.13$\pm$0.01~pc. The velocity structures of most filaments present continuous distributions with slight velocity gradients. We find that turbulence is the dominant internal pressure to support the fragmentation of filaments instead of thermal pressure. Most filaments have virial parameters smaller than 2; thus, they are gravitationally bound. Four filaments have an LTE line mass close to the virial line mass. We further extract dense clumps using the $^{13}$CO data and find that 64$\%$ of the clumps are associated with the filaments. According to the complementary IR data, most filaments have associated Class~II young stellar objects. Class~I objects are mainly found to be located in the filaments with a virial parameter close to 1. Within two virialized filaments, $^{12}$CO outflows have been detected, indicating ongoing star-forming activity therein.

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arXiv2019

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution - Survey Description and Compact Source Catalogue

We present the first release of the data and compact-source catalogue for the JCMT Large Program SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE). SCOPE consists of 850-um continuum observations of 1235 Planck Galactic Cold Clumps (PGCCs) made with the Submillimetre Common-User Bolometer Array 2 on the James Clerk Maxwell Telescope. These data are at an angular resolution of 14.4 arcsec, significantly improving upon the 353-GHz resolution of Planck at 5 arcmin, and allowing for a catalogue of 3528 compact sources in 558 PGCCs. We find that the detected PGCCs have significant sub-structure, with 61 per cent of detected PGCCs having 3 or more compact sources, with filamentary structure also prevalent within the sample. A detection rate of 45 per cent is found across the survey, which is 95 per cent complete to Planck column densities of $N_{H_{2}}$ $>$ 5 $\times$ 10$^{21}$ cm$^{-2}$. By positionally associating the SCOPE compact sources with YSOs, the star formation efficiency, as measured by the ratio of luminosity to mass, in nearby clouds is found to be similar to that in the more distant Galactic Plane, with the column density distributions also indistinguishable from each other.

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arXiv2019

The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg

The Milky Way Imaging Scroll Painting (MWISP) project is an unbiased Galactic plane CO survey for mapping regions of l=-10deg to +250deg and |b|<5.2deg with the 13.7 m telescope of the Purple Mountain Observatory. The legacy survey aims to observe the 12CO, 13CO, and C18O (J=1-0) lines simultaneously with full sampling using the nine-beam Superconducting SpectroScopic Array Receiver (SSAR) system with an instantaneous bandwidth of 1 GHz. In this paper, the completed 250 deg^2 data from l=+25.8deg to +49.7deg are presented with a grid spacing of 30" and a typical rms noise level of ~0.5 K for 12CO at the channel width of 0.16 km/s and ~0.3 K for 13CO and C18O at 0.17 km/s. The high quality data with moderate resolution (50"), uniform sensitivity, and high spatial dynamic range, allow us to investigate the details of molecular clouds (MCs) traced by the three CO isotope lines. Three interesting examples are briefly investigated, including distant Galactic spiral arms traced by CO emission with VLSR<0 km/s, the bubble-like dense gas structure near the HII region W40, and the MCs distribution perpendicular to the Galactic plane.

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arXiv2018

The Formation Conditions of the Wide Binary Class 0 Protostars within BHR 71

We present a characterization of the binary protostar system that is forming within a dense core in the isolated dark cloud BHR71. The pair of protostars, IRS1 and IRS2, are both in the Class 0 phase, determined from observations that resolve the sources from 1 um out to 250 um and from 1.3 mm to 1.3cm. The resolved observations enable the luminosities of IRS1 and IRS2 to be independently measured (14.7 and 1.7L_sun, respectively), in addition to the bolometric temperatures 68~K, and 38~K, respectively. The surrounding core was mapped in NH3 (1,1) with the Parkes radio telescope, and followed with higher-resolution observations from ATCA in NH3 (1,1) and 1.3cm continuum. The protostars were then further characterized with ALMA observations in the 1.3~mm continuum along with N2D+ (J=3-2), 12CO, 13CO, and C18O (J=2-1) molecular lines. The Parkes observations find evidence for a velocity gradient across the core surrounding the two protostars, while ATCA reveals more complex velocity structure toward the protostars within the large-scale gradient. The ALMA observations then reveal that the two protostars are at the same velocity in C18O, and N2H+ exhibits a similar velocity structure as NH3. However, the C18O kinematics reveal that the rotation on scales $<$1000~AU around IRS1 and IRS2 are in opposite directions. Taken with the lack of a systematic velocity difference between the pair, it is unlikely that their formation resulted from rotational fragmentation. We instead conclude that the binary system most likely formed via turbulent fragmentation of the core.

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arXiv2018

The Large-scale ISM of SS433/W50 Revisited

With new high-resolution CO and HI data, we revisited the large-scale interstellar medium (ISM) environment toward the SS 433/W50 system. We find that two interesting molecular cloud (MC) concentrations, G39.315-1.155 and G40.331-4.302, are well aligned along the precession cone of SS 433 within a smaller opening angle of ~7deg. The kinematic features of the two MCs at ~73--84 km/s, as well as those of the corresponding atomic-gas counterparts, are consistent with the kinematic characteristics of SS 433. That is, the receding gas from SS 433 jet is probably responsible for the redshifted feature of G39.315-1.155 near the Galactic plane and the approaching one may power the blueshifted gas of G40.331-4.302 toward the observer. Moreover, the HI emission at VLSR~70--90 km/s displays the morphological resemblance with the radio nebula W50. We suggest that the VLSR=77\pm5 km/s gas is physically associated with SS 433/W50, leading to a near kinematic distance of 4.9\pm0.4 kpc for the system. The observed gas features, which are located outside the current radio boundaries of W50, are probably the fossil record of jet-ISM interactions at ~10^5 years ago. The energetic jets of the unique microquasar have profound effects on its ISM environment, which may facilitate the formation of molecular gas on the timescale of <0.1 Myr for the ram pressure of ~2x10^6 K cm-3.

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