PII References

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Contents 1 Moritz et al 1998 2 Mebold et al. 1985 3 Shull et al 2009 4 K. Gillmon and J. M. Shull, ApJ, 636:908–915, 2006 5 B. P. Wakker, ApJS, 163:282–305, 2006 6 Richter et al. 2003, ApJ, 586,230-248 7 Peregrine M. McGehee,2008, Handbook of Star Forming Regions Vol. II Astronomical Society of the Pacific 8 Wennmacher et al. 1992 9 Lallement et al. 2003 10 Lockman & Condon 2005 11 Herbstmeier et al. 1993 12 Herbstmeier et al. 1994 13 Johnson ApJ 309, 321 14 Danner,1998, A&A, 128,331 15 Johnson and Klemola ApJS 63, 701, 1987 16 Rohlfs et al. A&A 211, 402 1989 17 Kerp et al. A&A 268, L21 1993 18 Kerp et al. A&A 286, L13, 1994 19 Wang & Yu AJ 109, 69 20 Welsh et al. A&A 308, 428 21 Miville-Deschenes et al. ApJ 631, L57 2005 22 Akeson & Blitz,1999, ApJ, 523,163-170 23 Lilienthal et al. 1991, A&A, 250, p.150-158 24 Boulanger & Perault, 1988, ApJ,330, 964--985 25 Park et al. 2009 ApJ 700, 155 26 Sasseen & Deharveng ApJ 469, 961

[edit] Moritz et al 1998

X-ray shadows of the Draco nebula-A new method to determine total hydrogen column densities

1. X-ray absorbing column densities at the deepest X-ray shadows are up to about 3x10²⁰ cm⁻² larger than the observed H I column densities
2. At the edge towards low galactic latitudes and longitudes, up to 70% of the hydrogen is in molecular form. In other parts of the nebula the molecular abundance is < 25%.
3. Found FIR-emissivity per hydrogen nucleon (H I + 2H₂ ) of about 1.0 10⁻²⁰ MJy/sr cm² in the draco region which is close to the mean value for the galactic cirrus (0.86 10⁻²⁰ MJy/sr cm² ).
4. Also found the FIR-emissivity per H I atom is varying strongly across the nebula.
5. In the draco region, 0.34 < xW(CO) < 0.52 10²⁰ cm−2 (K km s−1 )−1 , similar to other cirrus clouds but a very low xW(CO) ratio of 0.17 cm−2 (K km s−1 )−1 at the edge of the Draco nebula towards low galactic coordinates where the CO abundance could be altered in a low-velocity shock.

[edit] Mebold et al. 1985

The Draco Nebula: A molecular cloud in the galactic halo.

1. l = 91; b = 38
2. HI, CO, H₂CO absorption
3. d= 800 pc
4. Goerigk et al. A&A 120, 63
   1. HI emission correlated with bright nebula.
   2. E(B-V) < 0.3 mag
   3. gas-to-dust ratio lower
   4. 11' x 11' squares
5. Regions of the Nebula with strong CO emission are side by side to pure HI regions (Mebold et al 1989)
6. Parts of the nebula are interacting with HVCs (Mebold et al 1990).
7. H₂ column around 1.2x10²¹

[edit] Shull et al 2009

A large reservoir of ionized gas in the Galactic halo: Ionized Silicon in HVC and IVC clouds

1. HST & FUSE observations used

[edit] K. Gillmon and J. M. Shull, ApJ, 636:908–915, 2006

Molecular Hydrogen in Infrared Cirrus. (UV absorbers Technique)

1. High dust/HI ratio, termed as "infrared excess", has been attributed to the presence of H2 by several authors (de Vries et al 1987; Desert et al. 1988; Reach et al. 1994; Moritz et al. 1998; Schlegel et al. 1998 etc)
2. Some of the IR cirrus cloud cores contain CO gas.
3. H2 is over 10⁴ times more abundant than CO.
4. Clear correlation between UV (H2) absorption and IR (cirrus) emission indicates that a significant fraction of H2 is physically associated with cirrus clouds.
5. H2 contained in most diffuse cirrus clouds.
6. At gb > 30 deg, ~ 50% of the sky is covered with cirrus at temperature corrected 100 micron intensities >= 1.5 MJy/sr.
   1. H2 in the cirrus contains ~ 3000 x M_sun
7. Milky Way disk-halo interface within the solar circle contains:
   1. H2 mass in cirrus ~ 10⁷ x M_sun
   2. Total Hydrogen Mass ~ 10⁸ x M_sun
8. Self-shielding Transition of H2 is visible:
   1. within the temperature corrected IR 100 range: 1.5 -- 3.0 MJy/sr
   2. N(H) >= 10^20.4 cm^-2(i.e., 2.5 x 10²⁰) & N(H2) >= 10^18.5 cm^-2 (i.e., 3.16 x 10¹⁸)(Gillmon et al 2006a)
   3. From IR excess technique of Reach et al (1994) the transition occurs at N(H) ~ 4 x 10²⁰ cm^-2.
   4. Molecular fraction above this transition varies between 1% -- 30%
9. IR cirrus clouds may actually have higher molecular fractions than the diffuse clouds in the Galactic disk.

[edit] B. P. Wakker, ApJS, 163:282–305, 2006

A FUSE Survey of High-Latitude Galactic Molecular Hydrogen.

1. H2 is a trace constituent of the ISM where N(HI) is > 8 x 10¹⁹ cm^-2.
2. H2 in the North Galactic Sky is shown in Fig. NGS. N(H2) is generally below 10¹⁷ cm^-2 for most latitudes above 45 deg except toward PG 1211+143.
   

   

   Fig. NGS
   

   

   Fig. SGS
3. H2 in the SGS is shown in Fig. SGS.
   1. In the SGS, higher N(H2) sight lines concentrate between l=40 deg & 150 deg (around l=90 deg).
   2. N(H2) shows no correlation with latitude.
4. Intermediate velocity H2 is also detected toward half of the intermediate velocity HI regions with the molecular fraction increasing toward higher N(HI).
5. Strong correlations between N(H2) and T01, the excitation temperature of the H2, as well as between N(H2) and the level population ratios (log [N(J')/N(J )])
6. H2 Detections in 16 intermediate-velocity clouds in the Galactic halo (out of 35 IVCs).
7. H2 is seen only in one high-velocity cloud (NGC 3783, the Leading Arm of the Magellanic Stream) out of the 19 high velocity HI clouds, which strongly suggests that dust is rare or absent in HVCs.
8. H2 detections in the disk of 5 external galaxies: NGC 4319, M33, NGC 625, NGC 5236 (=M83), and Mrk 153.

[edit] Richter et al. 2003, ApJ, 586,230-248

A Far Ultraviolet Spectroscopic Explorer Survey of Molecular Hydrogen in Intermediate-Velocity Clouds in the Milky way Halo

1. Study of FUSE observations reveals that diffuse molecular hydrogen is a widespread, but not very abundant constituent in IVC's in the low Galactic halo.
2. H2 in IVC's resides in a large number of small (D ~ 0.1 pc) relatively dense (n_H ~ 30 cm^-3) filaments associated with the CNM in the clouds.
3. difficult to detect such regions in H2 absorption because of their small size.
4. Molecular hydrogen is able to form and survive in regions with low HI column densities.
5. Key point for the formation & survival of H2 in IVC's is that the presence of heavy elements & dust grains and moderate FUV radiation field in the cloud.
6. Evidence exist for the presence of H2 in IVC
7. Non detection of H2 in HVC complex C even with N(HI) of 1 x 10²⁰ cm^-2 down to the level of N(H2) = 1 x 10¹⁴ cm^-2. This could be because of the low metallicity in Complex C.

[edit] Peregrine M. McGehee,2008, Handbook of Star Forming Regions Vol. II Astronomical Society of the Pacific

Star Formation and Molecular Clouds at High Galactic Latitude

1. high latitude population of molecular clouds is mostly translucent due to their proximity to the Sun
2. molecular cores have been identified in translucent clouds and even in Galactic cirrus
3. Draco Intermediate Velocity Clouds (MBM 41–44) vlsr = −21 km/s
4. Distance estimates based on Na I D absorption suggesting 463⁺¹⁹²₋₁₃₆ to 618⁺²⁴³₋₁₇₄ pc (Gladders et al. 1998).
5. Star count analyzes and reddening studies have resulted in significantly greater distance estimates including 800 to 2500 pc (Goerigk & Mebold 1986), and 800 to 1300 pc (Penprase et al. 2000).

[edit] Wennmacher et al. 1992

A very dense H I filament within the Local Hot Bubble.

1. LVC 88+36-2 (Lilienthal & Wennmacher 1990), also known as "Finger filament".
   1. at least 6 deg elongated filament along the GPA 50 deg.
   2. tip of the filament [located at (l,b) = (90^o, 38.5^o)] overlaps with the Draco Nebula
   3. Maximum T_B 30 K is found at (l,b) = (87.5^o, 36^o); corresponding N(HI) is 1.4 x 10²⁰ /cm²
2. Local Hot Bubble radius in this direction is d 100 pc
3. Na I D absorption line of stars towards this direction set the upper limit of the distance to this cloud at 60 20 pc, implies LVC 88+36-2 located within the LHB.
4. X-ray shadows.

[edit] Lallement et al. 2003

3D mapping of the dense interstellar gas around the Local Bubble.

1. MBM 41-43 clouds are located at the neutral boundary of the Bubble.
2. closest dense and cold gas "wall" with an equivalent N(HI) ~ 3 x 10¹⁹ /cm² in the 1^st quadrant is at ~ 55-60 pc.
3. dense HI cloud in the direction of MBM 41-43 is seen at < 85 pc.

[edit] Lockman & Condon 2005

The SIPTZER Space Telescope First Look Survey: Neutral Hydrogen Emission.

1. Imaged 21 cm HI emission using 100 m GBT over a 3^o x 3^o square centered on (l,b) = (88.32^o, 34.89^o) with an angular resolution 9.8'.
2. HI spectra in the FLS field typically contain 4 components:
   1. a broad line near zero velocity that contains most of the emission in most directions
   2. a bright narrow line also near zero velocity that has a patchy although spacially correlated structure
   3. several IVC's with negative velocities and
   4. a HVC.
3. HI emission shows strong correlation with dust except for HVC.
4. Average column density, N(HI) = 2.5 × 10²⁰ cm^-2 with an RMS fluctuation of 0.3 × 10²⁰ cm^-2.
5. Galactic H I in the region consists of a high-velocity cloud, several intermediate-velocity clouds (one of which is probably part of the Draco Nebula), and narrow-line low-velocity filaments.
6. Regions with peak H I line brightness temperature (not the total N(HI)) directions, where Tb > 12 K have E(B - V)/NH I significantly above the average value.
7. Relatively high E(B-V)/N(HI) ratios in such directions suggest the presence of molecular gas.
8. The arc of HI emission (ridge) arises in a narrow line at V_LSR = -2 km/s which is the brightest line in the field with a peak T_b = 26 K corresponding to Tau_HI 0.4.
9. In our GALEX field
   1. 1.8 x 10²⁰ <= N(HI) < 3.2 x 10²⁰ /cm²
   2. 0.02 < E(B-V) < 0.05 mag; 1 x 10^-22 < E(B-V)/N(HI) <= 1.5 x 10^-22 mag cm²
10. directions in which the 21 cm line has a peak brightness Tb >= 12 K ( e.g., dust ridge area) show above average E(B-V)/N(HI) ratio and may contain some H2.
11. Mean dust-to-gas ratio derived in the FLS field from Schlegel et al. (1998) reddening values implies that 1 mag of reddening requires an N(HI) of 8.6 x 10²¹ /cm², which is almost 50% higher than the canonical value of 5.8 x 10²¹ /cm² (Bohlin et al. 1978) resulted from direct observations in UV and optical.

[edit] Herbstmeier et al. 1993

1. Region studied l(89 -- 96 deg) b(36 -- 42 deg)
2. Draco Nebula also called IVC G91.0 +38.0 (VSLR=-21); IVC 91+38-21; LBN 406, 412, 415; MBM 41, 42, 43, 44 AND G 90.0+38.8, G 94.8 +37.6
3. Draco Nebula located near the IAU HI baseline position B8(l-90, b=40) which is characterized by a low HI column density and is well separated from fore- and background gas.
4. Mean visual extinction: 0.02 <A_v> 0.06 mag
5. Maximum N(H) < 3.7 x 10²⁰ /cm²
6. Molecular fraction in the Draco region: 0.04 <f_Mol> 0.7
7. FIR emissivities (I₁₀₀/N(H)) in most regions of the Draco Nebula are larger than 1.0 x 10^-20 MJy/sr cm², the mean value found for the galactic cirrus clouds.
   1. emissivity high in the HI halos than in the molecular cores.
8. I₆₀/I₁₀₀ micron ratio
   1. within the molecular cloud: < 0.15
   2. within the HI regions: > 0.2
9. Outside the molecular cloud, I_100,DBG = (0.88 0.04) x 10^-20 N(HI) (MJy/sr cm²) + (1.42 0.08) MJy/sr with a correlation coefficient of 0.95
10. IR 100 emission from the Draco Nebula is between 0.3 to 4.0 MJy/sr.
11. X_W(CO) in the Draco Nebula: 0.02x10²⁰ < X_W(CO) < 0.26x10²⁰ cm^-2/(K km/s), more than a factor of 10 smaller than in the galactic plane and in most other cirrus clouds.
    1. Near galactic plane: 1.6 x 10²⁰ < X_W(CO) < 2.3 x 10²⁰ cm^-2/(K km/s) (Strong et al 1988; Bloemen et al. 1990)
    2. For diffuse and translucent clouds of the galactic cirrus: X_W(CO) = 0.5 x 10²⁰ cm^-2/(K km/s) (de Vries et al. 1987)
12. From the whole Draco Region:
    1. N(HI) - I100 correlation is 66%
    2. N(HI) - W(¹²CO) correlation is 35%
    3. I100 - W(¹²CO) correlation is 67%
13. Significant differences in the coefficients such as correlation, slope and offset values between the emissions, IR100, N(HI) & W(CO) found in different part of the nebula.

[edit] Herbstmeier et al. 1994

1. Clouds showing no CO line emission do contain molecular hydrogen (Martin et al. 1990)
2. Blitz et al (1990) conclude that most of the FIR excess clouds defined by Desert et al (1988) are molecular clouds without associated CO emission.
3. Blitz et al (1990) derive a lower IRAS 100 micron limit of 4 MJy/sr for the detectability of CO.

[edit] Johnson ApJ 309, 321

1. Draco: clumpy structure.

[edit] Danner,1998, A&A, 128,331

Searching for old neutron stars with ROSAT. I.

1. Magnani, Blitz and Mundy, hereafter MBM, (1985): MBM 41-44 Cloud complex casts cleanest and deepest shadowsa deep shadow on the diffuse soft X-ray background. The absorption contours in the X-ray image accurately trace the areas of emission on the IRAS image (see Fig.shadow).
   

   

   Fig.shadow
2. The IRAS image shows that the apparently isolated peaks of CO emission (Magnani et al. 1985) belong in fact to the same structure.
3. Magnani, Blitz and Mundy, hereafter MBM, (1985) Clouds details:
   1. density range: 35 to 500 cm^-3 with a mean value of 140 cm^-3
   2. average distance to the clouds is 105 pc
   3. mean radius of a cloud is 1.7 pc
   4. velocity dispersion is 5.6 1.2 km/s
   5. mean velocity wrt the local standard of rest is 0.13 0.11 km/s

[edit] Johnson and Klemola ApJS 63, 701, 1987

[edit] Rohlfs et al. A&A 211, 402 1989

1. Small scale filament with CO data.
2. Possible collision of Draco cloud with HVC.

[edit] Kerp et al. A&A 268, L21 1993

1. ROSAT observations to LVC 88+36-2
2. T < 150 K
3. nh > 75 cm-3
4. column density of 1.6 - 1.9 x 10²⁰ cm-2

[edit] Kerp et al. A&A 286, L13, 1994

1. ROSAT observations of HVC 90.5+42.5-130
2. X-ray emission from edges due to HVC interacting with galactic gas.

[edit] Wang & Yu AJ 109, 69

1. Degree size X-ray absorbing clouds at distances of 100 pc or so.

[edit] Welsh et al. A&A 308, 428

1. No high velocity components to Chain A.
   1. Distance > 800 pc.
2. Low velocity absorption.

[edit] Miville-Deschenes et al. ApJ 631, L57 2005

The First Detection of Dust Emission in a High-Velocity Cloud

1. Spitzer observation of dust in Complex C.
2. Complex C represents the infall of intergalactic material onto the Milky Way
   

   
3. XFLS field is located on the edge of Complex C, a high-velocity gas structure spanning more than 1500 deg2 on the sky.
4. Complex C is a large HVC (roughly 20^o x 90^o) and is at least ~5 kpc away (van Woerden et al. 1999).
   1. subsolar metallicity (0.1-0.3; Tripp et al. 2003)
   2. contains ionized gas observed in H emission (Tufte et al. 1998) and O VI absorption (Sembach et al. 2003)
   3. FUSE observations detected OVI emission from Complex C; x-ray emission & H_alpha emission are also detected towards Complex C (Otte & Dixon, 2006)
   4. located at a distance greater than 5 kpc from the Sun (Wakker 2001)
   5. iron abundances in the HVC indicate that Complex C contains little or no dust (Tripp et al. 2003)
5. The column density of the HVC layer is (2-4) × 10¹⁹ cm^-2 in the XFLS field
6. T = 10.7 K; much colder than ISM 17.5 K.
7. Small molecular clouds spatially correlated with HI but small filling factor.
8. HVC largely molecular rather than diffuse.
9. Correlation of IR with HVC.

[edit] Akeson & Blitz,1999, ApJ, 523,163-170

A search for atomic hydrogen and molecular gas absorption in high-velocity clouds

1. HVCs cover more than 15% of the sky and are seen at both negative and positive velocities (Hulsbosch & Wakker (1988) and Bajaja et al. (1985))
2. HVC towards RA(16 37 17.42) DEC(+57 26 15.7) (l,b) => (86.64, 40.36)
   1. belongs to Complex C, the largest bona fide HVC whose distance is measured to be 4-10 kpc (van Woerden et al. 1999).
   2. From the observations at VLA, Total NH(I) = 3.5 x 10¹⁹ cm^-2
   3. From CO measurement N(H2) = 1.3 x 10¹⁹ cm^-2
   4. From HCO+, N(H2) range from 5 x 10¹⁹ to 2 x 10²⁰ cm^-2 using an abundance of [HCO+] = 5 x 10^-9.
   5. OVRO observations shows that N(HI) = 4.3 x 10¹⁹ cm^-2
   6. N(H2)/N(HI) = 0.37
3. HVCs are predominantly extragalactic objects. Reasons:
   1. sub solar metallicity toward complex C indicate that it is an accretion event of an extragalactic cloud
   2. pressure measured toward HVCs is 4 orders of magnitude less than that in the mid plane of MW near the Sun suggest that it is self-gravitating extragalactic HVC.
4. The HI columns toward the observed HVCs are below the threshold value (5 x 10²⁰ cm², Savage et al. 1977) for H2 formation in clouds within the Galaxy but the uncertainties in the peak column density on small scales and in the incident radiation field mean that the existence of some molecular material within HVCs cannot be ruled out.
5. HVCs do not contain significant amounts of cold CO gas. If CO traces H in HVCs, the average upper limit on molecular gas is 10¹⁹ cm^-2.
6. CO/H2 Ratio is low: HVCs may contain H2 without observing CO because very low metallicities of HVCs or the molecules are depleted onto grains, CO absorption would not be observed.
7. HVCs are weak HI and molecular gas absorbers.

[edit] Lilienthal et al. 1991, A&A, 250, p.150-158

Interstellar NA I D line studies of stars towards the Draco nebula

1. Two spatially separated gas clouds - LVC 88+36-2 (d~ 60pc) & Draco Nebula (d>300pc)
2. No physical relation

[edit] Boulanger & Perault, 1988, ApJ,330, 964--985

Diffuse Infrared Emission from the Galaxy. I. Solar Neighborhood

1. Basic properties of IR emission from the ISM are derived from this study.
2. IR emission correlates with the HI gas column density only outside molecular clouds and away from heating sources.
3. Dust in molecular clouds (MC) not associated with HII regions is heated by the external radiation field
4. embedded stars have a negligible contribution to their IR emission
5. away from internal sources of heating, IR 100 micron emission from MCs is correlated with the column density of gas up to Av of ~ 3 mag.
6. Origin of IR emission:
   1. stars younger than a few 10^8 yr are responsible for (2/3)rd of the IR emission from the solar neighborhood.
   2. most of this emission comes from ISM not associated with the current star formation
7. outside the star forming regions, the IR emission is dominated by the external heating, and correlates with the CO emission (e.g, good correlation in Chamaeleon II & bad correlation in Orion A region)
8. IR(nu)/N(H) ratio is very much depend on the region

[edit] Park et al. 2009 ApJ 700, 155

1. Observation of Draco cloud: [IVC G90.0 +38.0 (VLSR ∼ −21 km s−1)].
2. Observed in CO by MBM.
3. Casts X-ray shadow.
4. 463 pc < d < 618 pc
5. Very little overlap with our observations.
6. Faint dust scattering.
7. Detected CIV, Si II*, OIII & H2 emissions inside the Draco cloud.
8. Detected CIV & Si II* emissions outside the Draco cloud.
9. CIV emission of 6000 LU outside Draco cloud.
10. H2 emission map generally correlates with H2 distribution, N(HI) and dust emission.
11. FUV continuum follows IR.
12. H2 fluorescent emission different from FUV. Attributed to radiation field.
13. Turbulent mixing layers of cold and hot gases in the Galactic halo heat the surrounding gases up to T~10⁵ - 10^5.5 k and produce emission lines such as CIV, OIII], OVI and H\alpha lines strongly in the UV & optical bands (Slavin et al 1993)
14. SiII* emission, is bright outside the Draco with extremely low emission inside the cloud, which is originating from the hot and warm ionized media located beyond the cloud.
15. The densest core of the cloud is rather bright in SiII* emission map which they are explained as the contribution from HII region (LBN 406; Lynds 1965) which can radiate SiII* emission.
16. H2 fluorescent emission correlates with N(H2), N(HI) & IR emission

[edit] Sasseen & Deharveng ApJ 469, 961

1. Small scale variation in the data. Spatial resolution of 3' but analysis done with 0.5 degree squares.
2. UV increases with IR.
3. UV/IR ratio different in different regions.