A HIGH-RESOLUTION STUDY OF THE H I-H<sub>2</sub>TRANSITION ACROSS THE PERSEUS MOLECULAR CLOUD

Lee, Min Young; Stanimirović, Snežana; Douglas, K. A.; Knee, L. B. G.; Francesco, James Di; Gibson, Steven J.; Begum, Ayesha; Grcevich, Jana; Heiles, Carl; Korpela, E. J.; Leroy, Adam K.; Peek, J. E. G.; Pingel, N. M.; Putman, Mary E.; Saul, Destry

doi:10.1088/0004-637x/748/2/75

Cited by 90 publications

(216 citation statements)

References 84 publications

Supporting

Mentioning

170

Contrasting

Order By: Relevance

“…This corresponds to a neutral gas surface density of Σ HI ≈ 5 M pc −2 and a molecular hydrogen surface density Σ H2 ≈ 4.4 M pc −2 . These surface densities are very similar to what is seen across the Perseus molecular cloud from high spatial resolution emission observations (Lee et al 2012), despite the H i and H 2 surface densities being measured directly along a pencil beam line of sight in our study while derived from dust maps in the latter. This also shows that H i-to-H 2 transition in our high-z system is likely following the same physical processes as in our Galaxy.…”

Section: Discussionsupporting

confidence: 83%

“…High spatial resolution (sub-pc) studies exist for nearby molecular clouds such as the Perseus cloud. Lee et al (2012) observe relatively uniform H i surface density of Σ HI ∼ 6−8 M pc −2 around H 2 clouds, in agreement with the theoretical expectations based on H 2 microphysics at solar metallicity, assuming CNM a priori (Krumholz et al 2009) or not (Bialy et al 2015).…”

Section: Introductionsupporting

confidence: 90%

See 1 more Smart Citation

Discovery of a Perseus-like cloud in the early Universe

Noterdaeme

Krogager

Balashev

et al. 2017

A&A

View full text Add to dashboard Cite

We present the discovery of a molecular cloud at z abs ≈ 2.5255 along the line of sight to the quasar SDSS J 000015.17+004833.3. We use a high-resolution spectrum obtained with the Ultraviolet and Visual Echelle Spectrograph together with a deep multi-wavelength medium-resolution spectrum obtained with X-shooter (both on the Very Large Telescope) to perform a detailed analysis of the absorption lines from ionic, neutral atomic and molecular species in different excitation levels, as well as the broad-band dust extinction.We find that the absorber classifies as a Damped Lyman-α system (DLA) with log N(H i) (cm −2 ) = 20.8 ± 0.1. The DLA has supersolar metallicity (Z ∼ 2.5 Z , albeit to within a factor of two to three) with a depletion pattern typical of cold gas and an overall molecular fraction f = 2N(H 2 )/(2N(H 2 ) + N(H i)) ∼ 50%. This is the highest f -value observed to date in a high-z intervening system. Most of the molecular hydrogen arises from a clearly identified narrow (b ∼ 0.7 km s −1 ), cold component in which carbon monoxide molecules are also found, with log N(CO) ≈ 15. With the help of the spectral synthesis code Cloudy, we study the chemical and physical conditions in the cold gas. We find that the line of sight probes the gas deep after the H i-to-H 2 transition in a ∼4−5 pc-size cloud with volumic density n H ∼ 80 cm −3 and temperature of only 50 K. Our model suggests that the presence of small dust grains (down to about 0.001 µm) and high cosmic ray ionisation rate (ζ H ∼ a few times 10 −15 s −1 ) are needed to explain the observed atomic and molecular abundances. The presence of small grains is also in agreement with the observed steep extinction curve that also features a 2175 Å bump. Interestingly, the chemical and physical properties of this cloud are very similar to what is seen in diffuse molecular regions of the nearby Perseus complex, despite the former being observed when the Universe was only 2.5 Gyr old. The high excitation temperature of CO rotational levels towards J0000+0048 betrays however the higher temperature of the cosmic microwave background. Using the derived physical conditions, we correct for a small contribution (0.3 K) of collisional excitation and obtain T CMB (z = 2.53) ≈ 9.6 K, in perfect agreement with the predicted adiabatic cooling of the Universe.

show abstract

Section: Discussionsupporting

confidence: 83%

Section: Introductionsupporting

confidence: 90%

Discovery of a Perseus-like cloud in the early Universe

Noterdaeme

Krogager

Balashev

et al. 2017

A&A

View full text Add to dashboard Cite

show abstract

“…The last free parameter is the metallicity Z. This model is supported by extragalactic observations (Krumholz et al 2009) as well as observations in the Perseus molecular cloud by Lee et al (2012). They find a uniform H  column density of N H  ∼ 6−8 M pc −2 for H 2 column densities up to N H 2 ∼ 80 M pc −2 .…”

Section: Column Density Threshold For Atomic Hydrogensupporting

confidence: 59%

“…Hence, we can estimate the column density directly from the measured brightness temperature T B . This method is used in several studies and is well described in the literature (e.g., Lee et al 2012;Motte et al 2014;Wilson et al 2010). Below, we discuss its limitations and describe a procedure to overcome them.…”

Section: Optically Thin H I Emissionmentioning

confidence: 99%

THOR: The H i, OH, Recombination line survey of the Milky Way

Bihr

Beuther

Ott

et al. 2015

A&A

View full text Add to dashboard Cite

To study the atomic, molecular, and ionized emission of giant molecular clouds (GMCs) in the Milky Way, we initiated a large program with the Karl G. Jansky Very Large Array (VLA): "THOR: The H , OH, Recombination line survey of the Milky Way". We map the 21 cm H  line, 4 OH lines, up to 19 Hα recombination lines and the continuum from 1 to 2 GHz of a significant fraction of the Milky Way (l = 15• −67• , |b| ≤ 1 • ) at an angular resolution of ∼20 . Starting in 2012, as a pilot study we mapped 4 square degrees of the GMC associated with the W43 star formation complex. The rest of the THOR survey area was observed during 2013 and 2014. In this paper, we focus on the H  emission from the W43 GMC complex. Classically, the H  21 cm line is treated as optically thin with properties such as the column density calculated under this assumption.This approach might yield reasonable results for regions of low-mass star formation, however, it is not sufficient to describe GMCs. We analyzed strong continuum sources to measure the optical depth along the line of sight, and thus correct the H  21 cm emission for optical depth effects and weak diffuse continuum emission. Hence, we are able to measure the H  mass of this region more accurately and our analysis reveals a lower limit for the H  mass of M = 6.6 −1.8 × 10 6 M (v LSR = 60−120 km s −1 ), which is a factor of 2.4 larger than the mass estimated with the assumption of optically thin emission. The H  column densities are as high as N H  ∼ 150 M pc −2 ≈ 1.9 × 10 22 cm −2 , which is an order of magnitude higher than for low-mass star formation regions. This result challenges theoretical models that predict a threshold for the H  column density of ∼10 M pc −2 , at which the formation of molecular hydrogen should set in. By assuming an elliptical layered structure for W43, we estimate the particle density profile. For the atomic gas particle density, we find a linear decrease toward the center of W43 with values decreasing from n H  = 20 cm −3 near the cloud edge to almost 0 cm −3 at its center. On the other hand, the molecular hydrogen, traced via dust observations with the Herschel Space Observatory, shows an exponential increase toward the center with densities increasing to n H 2 > 200 cm −3 , averaged over a region of ∼10 pc. While atomic and molecular hydrogen are well mixed at the cloud edge, the center of the cloud is strongly dominated by H 2 emission. We do not identify a sharp transition between hydrogen in atomic and molecular form. Our results, which challenge current theoretical models, are an important characterization of the atomic to molecular hydrogen transition in an extreme environment.

show abstract

“…This effect might induce a lower formation rate of the molecular gas phase, producing thus molecular gas poor cluster galaxies. The timescale for molecular gas formation on dust grains is indeed quite short, of the order of 10−30 Myr (Liszt 2007;Goldsmith et al 2007;Lee et al 2012). This phenomenon, however, would not affect the dust component associated to the molecular gas and thus does not explain the observed truncation of the far-infrared radial profiles of Hi-deficient latetype galaxies in the Virgo cluster (Cortese et al , 2012b.…”

Section: Molecular Gas Formationmentioning

confidence: 99%

Cold gas properties of theHerschelReference Survey

Boselli

Cortese

Boquien

et al. 2014

A&A

177

250

View full text Add to dashboard Cite

The Herschel Reference Survey is a complete volume-limited, K-band-selected sample of nearby objects including Virgo cluster and isolated objects. Using a recent compilation of Hi and CO data for this sample we study the effects of the cluster environment on the molecular gas content of spiral galaxies. With the subsample of unperturbed field galaxies, we first identify the stellar mass as the scaling variable that traces the total molecular gas mass of galaxies better. We show that, on average, Hi-deficient galaxies are significantly offset (4σ) from the M(H 2 ) vs. M star relation for Hi-normal galaxies. We use the M(H 2 ) vs. M star scaling relation to define the H 2 -deficiency parameter as the difference, on logarithmic scale, between the expected and observed molecular gas mass for a galaxy of given stellar mass. The H 2 -deficiency parameter shows a weak and scattered relation with the Hi-deficiency parameter, here taken as a proxy for galaxy interactions with the surrounding cluster environment. We also show that, as for the atomic gas, the extent of the molecular disc decreases with increasing Hi-deficiency. All together, these results show that cluster galaxies have, on average, a lower molecular gas content than similar objects in the field. Our analysis indicates that ram pressure stripping is the physical process responsible for this molecular gas deficiency. The slope of the H 2 − de f vs. Hi − de f relation is less than unity, while the D(Hi)/D(i) vs. Hi − de f relation is steeper than the D(CO)/D(i) vs. Hi − de f relation, thereby indicating that the molecular gas is removed less efficiently than the atomic gas. This result can be understood if the atomic gas is distributed on a relatively flat disc that is more extended than the stellar disc. It is thus less anchored to the gravitational potential well of the galaxy than the molecular gas phase, which is distributed on an exponential disc with a scalelength r CO 0.2r 24.5 (g). There is a clear trend between the NUV-i colour index, which is a proxy for the specific star formation activity, and the H 2 -deficiency parameter, which suggests that molecular gas removal quenches the activity of star formation. This causes galaxies migrate from the blue cloud to the green valley and, eventually, to the red sequence. The total gas-consumption timescale of gas deficient cluster galaxies is comparable to that of isolated, unperturbed systems. The total gas depletion timescale determined by considering the recycled fraction is τ gas,R 3.0−3.3 Gyr, which is significantly larger than the typical timescale for total gas removal in a ram pressure stripping process, indicated by recent hydrodynamical simulations to be τ RP 1.5 Gyr. The comparison of these timescales suggests that ram pressure, rather than a simple stop of the infall of pristine gas from the halo, will be the dominant process driving the future evolution of these cluster galaxies.

show abstract

A HIGH-RESOLUTION STUDY OF THE H I-H₂TRANSITION ACROSS THE PERSEUS MOLECULAR CLOUD

Cited by 90 publications

References 84 publications

Discovery of a Perseus-like cloud in the early Universe

Discovery of a Perseus-like cloud in the early Universe

THOR: The H i, OH, Recombination line survey of the Milky Way

Cold gas properties of theHerschelReference Survey

Contact Info

Product

Resources

About

A HIGH-RESOLUTION STUDY OF THE H I-H2TRANSITION ACROSS THE PERSEUS MOLECULAR CLOUD

Cited by 90 publications

References 84 publications

Discovery of a Perseus-like cloud in the early Universe

Discovery of a Perseus-like cloud in the early Universe

THOR: The H i, OH, Recombination line survey of the Milky Way

Cold gas properties of theHerschelReference Survey

Contact Info

Product

Resources

About

A HIGH-RESOLUTION STUDY OF THE H I-H₂TRANSITION ACROSS THE PERSEUS MOLECULAR CLOUD