OH Masers and the Dust Emissions Towards High Mass Protostellar Objects
AAstronomy & Astrophysics manuscript no. OH-mmtex-arXiv November 21, 2018(DOI: will be inserted by hand later)
OH Masers and the Dust Emissions Towards HMPOs
K. A. Edris
Astronomy Dept., Faculty of science, Al-Azhar University, Naser City, Cairo, Egyptthe date of receipt and acceptance should be inserted later
Abstract.
Context . OH maser emission is known to be associated with high mass star forming regions. Towards some of these regions,OH masers are associated with HII regions. Towards others, believed to be in an earlier evolutionary state, OH masers are o ff setfrom HII regions. Towards these later regions, it is believed that OH masers are associated with the circumstellar disk (e.g. Edriset al. 2005; Gray et al. 2003). These disks should be hosting dense dust grains. The presence of the hot dust could be traced viathe millimeter continuum emission as well as IR emission. Aims . studying the association between millimeter (mm) continuum, the OH masers emission, and IRAS sources.
Methods . A sample of 27 High Mass Star Forming Regions (HMSFRs) chosen from IRAS catalog and show OH maser emission(Edris et. al. 2007) have been studied at 1.1 millimeter (mm) continuum emission of the Bolocam Galactic Plane Survey(BGPS).
Results . The 1.1-mm continuum emission have been found within (cid:39) (cid:48) towards 23 sources of the OH maser sample. Thesesources were divided into three groups depends on the o ff set of the closest mm peak from the OH maser position. The associ-ation between the OH, mm and IR emissions types have been confirmed for two sources. Generally the IRAS position is moreconsistent with the mm peaks than the OH maser emission and towards 10 sources the IRAS and OH masers are not consistentwith the same mm peak. Conclusion . The relatively large positional uncertainty do not allow to firm conclusions but it seems that the IR peak is closerto the mm emission than the OH maser.
Key words. stars: formation, masers: OH masers, millimeter
1. Introduction
Compact HII regions, molecular outflows and circumstel-lar disks are signs of the existence of massive protostars(e.g. Garay & Lizano 1999; Churchwell 2002). Maseremission is also found to be associated with these ob-jects (e.g. Garay & Lizano 1999; Edris et al. 2005) withOH one of most widespread types of maser associatedwith these regions. OH masers are associated with twodi ff erent stages of star formation. The first one is asso-ciated with circumstellar disks and molecular outflows(Cohen, Rowland & Blair 1984; Brebner 1988; Cohenet al. 2003; Edris et al. 2007). the other one is a rela-tively advanced star forming stage of the appearance ofUCHII region (e.g. Garay & Lizano 1999, and referencestherein). The mm emission could trace di ff erent phenom-ena of star formation process. It could trace slowly col-lapsing rotating molecular fragment onto itself, a circum-stellar disk and molecular outflows (e.g. Zinnecker et al.1992 ; Adams et al. 1990 ; Beuther et al 2002b). thereforethe mm emission should be associated with the first type Send o ff print requests to : [email protected] of OH masers mentioned above. The association betweenthe maser emission and mm and sub-mm have studied incase of methanol masers by Breen et al. (2010) and watermasers by Jenness et al. (1995). The association of OHmasers and the mm emission has not been studied. Withthis in mind a sample of high mass protostellar objectshas been studied at the mm emission.
2. The sample
The sample of sources in this present paper is partiallydrawn from the surveys of Sridharan et al. (2002) andMolinari et al. (1996). These two samples are originallydrawn from the IRAS Point Source Catalog based ontheir colour selection criteria. They are believed to con-tain massive sources in a very early stage of evolutionprior to the forming of UCHII regions. Molinari et al.(1996) divided their sample into two types:
High and
Low sources. The Sridharan et al. (2002) sample and the
High sources of Molinari et al (1996) have similar colour. Theyboth satisfy the criteria of Wood & Churchwell (1989)for a UCHII region colour. However the sources in these a r X i v : . [ a s t r o - ph . GA ] J u l K. A. Edris: OH Masers and the Dust Emissions Towards HMPOs two samples (as well as the Molinari et al. (1996)
Low sources) are not known to be associated with detectableHII regions. Molinari et al. (1996) suggest that their
Low sources comprises objects which are in a di ff erent evolu-tionary stage from those in their High sources, and there-fore also from the other sample. Further details aboutthese sources and their selection criteria can be found inSridharan et al. (2002) and Molinari et al. (1996) and ref-erences therein as well as their follow up papers.Edris, Fuller & Cohen (2007, hereafter EFC07) sur-veyed these two samples for OH maser emission and de-tected the masers towards 26 % of the sources. One ofthese sources (IRAS 20126 + High type sources and 6
Low type sources.
3. Observations and archive data
The Nanc¸ay radio telescope and the 100 − m single dishGreen Bank Telescope (GBT) have been used to observethe four OH transitions at 1665, 1667, 1612 and 1720MHz in both left and right circular polarizations. Afterconfirming the presence of an OH maser towards theIRAS position of a source, the GBT was used to map thesources small 3 arcmin sampled maps, typically 3 × The millimeter data is based on the Bolocam GalacticPlane Survey (BGPS). The used tables have been down-loaded from the http: // irsa.ipac.caltech.edu / data / . The sur-vey uses the 144-element Bolocam array on the CaltechSubmillimeter Observatory, which observes in a bandcentered at 268 GHz (1.1-mm) and a width of 46 GHz.The bandpass is designed to reject emission from theCO(2,1) transition, which is the dominant line contrib-utor at these wavelengths. Detailed description of theBGPS survey observations and methods can be found athttp: // irsa.ipac.caltech.edu / data. Fig. 1.
The o ff sets of the OH masers and the closest mm peak.
4. Results
Among the 27 OH maser sources, 23 sources have beenfound to be associated with many peaks of millimeteremission within 30 (cid:48) . The o ff sets of the closest mm peakhave been calculated. The o ff set of < ff set of two sources of them are ≤ + ff erent sam-ples of High Mass Protostellar Objects (HMPOs) candi-dates. IRAS 18089-1732 is one of the High type sampleof Molinari et al. 1996 while IRAS 19035 + + ff sets of the next 12 sources are 0.6 − ff sets ≥ High sources of Molinari et al. (1996) andone from the sample of Sridharan et al. (2002).positions maps for the 23 sources are shown in fig-ure (4 and 6) . Table 1 gives the parameters of the stud-ied sample, namely the source name, the type, the posi-tion of the OH maser emission, the position of the clos-est 1.1-mm peak, the distances of the sources, the o ff setof the two position in pc and the peak velocities of theOH sources. The OH masers positions are from the GBTobservations (Edris, Fuller, & Cohen 2007); these posi-tions have been drawn from the 1665-MHz line emission.Some sources which show di ff erent position for the 1667-MHz line, the position of the 1667-MHz line emission ismentioned as well. Their positions and rms errors havebeen calculated from 9 points maps. The distances of thesources have been taken from Molinari et al. (1996) andSridharan et al. (2002) except IRAS 19118 + . A. Edris: OH Masers and the Dust Emissions Towards HMPOs 3 Table 1.
The OH masers positions and the positions of the closest 1.1 mm emission. The OH positions are measured from GBTobservations (Edris, Fuller, & Cohen 2007) except for sources which have higher resolution observations their position have beentaken from. These sources are IRAS 18089-1732 and IRAS 19035 + + IRAS Name type OH masers position 1.1 mm position Distance O ff set peak velocityRA(J2000) DEC(J2000) RA(J2000) DEC(J2000) Kpc arcsec km sh m s ◦ (cid:48) (cid:48)(cid:48) h m s ◦ (cid:48) (cid:48)(cid:48) + ± ±
23 06 08 53 21 35 16 1.5 70 10.1417527 − ± −
24 36 36 ±
27 17 55 33 −
24 41 52 3.23 323 11.5318024 − ± −
21 14 59 ±
19 18 05 26 −
21 19 24 0.12 264 − − ± −
20 18 41 ±
38 18 07 46 −
20 19 47 4.99 68 44.3618089 − / S 18 11 51.4 ± −
17 31 29 ±
01 18 11 51 −
17 31 26 3.6 3 32.9218090 − ± −
18 29 47 ±
26 18 11 44 −
18 43 14 6.6 808 108.918102 − ± −
18 00 23 ±
16 18 13 11 −
17 59 48 2.6 110 24.4018144 − ± −
17 22 29 ±
16 18 17 15 −
17 12 08 4.33 644 48.3318182 − ± −
14 31 23 ±
14 18 21 09 −
14 31 45 4.5 22 61.5518236 − ± −
12 04 54 ±
14 18 26 39 −
12 04 53 2.51 48 31.0918 26 31.7 ± −
12 03 26 ±
14 18 26 26 −
12 03 57 2.51 92 62.4518278 − ± −
10 07 25 ±
17 18 30 37 −
10 07 57 5.7 33 119.718290 − ± −
09 22 14 ±
15 18 31 43 −
09 22 20 5.3 43 78.3318360 − ± −
05 36 25 ±
16 18 38 48 −
05 36 20 6.28 95 102.918 38 47.2 ± −
05 35 40 ±
17 18 38 48 −
05 36 20 6.28 44 105.318385 − ± −
05 08 57 ±
14 18 41 19 −
05 08 11 2 49 24.8718440 − ± −
01 44 27 ±
13 18 46 36 −
01 45 15 8.3 54 101.418454 − ± −
01 54 34 ±
15 18 48 01 −
01 53 47 5.6 47 39.618488 + / S 18 51 30.5 ± ±
16 18 51 36 00 02 58 5.4 92 79.5718527 + ± ±
40 18 56 03 02 56 54 5.26 1252 74.4418566 + / S 18 59 08.6 ± ±
17 18 59 10 04 12 18 6.7 119 83.4118 59 10.4 ± ±
14 18 59 10 04 12 18 6.7 63 81.5219035 + ± ±
01 19 06 02 06 46 37 2.2 4 32.4419092 + ± ±
06 19 11 39 08 46 30 4.48 8 57.8719118 + ± ±
46 19 14 14 09 50 33 246 61.2519410 + ± ±
12 19 43 11 23 44 20 2.1 21 20.67
Sources with OH masers but without millimeter emission + + + + K. A. Edris: OH Masers and the Dust Emissions Towards HMPOs
IRAS 06056 + . The OH masers were detected to-wards this source at 1665-, 1667-, and 1720-MHz lines.The velocity of the 1720-MHz OH satellite line is moreconsistent with the NH gas velocity (Molinari et al.1996) than the two OH main lines. The CO outflow mapof the region presented by Zhang et al. (2005) show atleast two outflows. The IRAS source is consistent withone of these outflows and the OH main lines may be con-sistent with the other. Several 1.1-mm peaks were de-tected towards this region mostly in the shape of bowshock (Figure 4). The peak seems to be closer to the OHmain lines is much weaker than the two peaks closer to theIRAS source. The velocity of the CH OH maser sourcedetected by Szymczak et al. (2000) is consistent with thevelocities of the OH maser main lines ( ∼
10 km s − ). Allthese indicate that this region is complex and contain atleast two protostars in di ff erent evolutionary stages. Thisis consistent with the near-IR K s band observations ofFaustini et al (2009) which suggest a cluster of severalmembers with a radius of 0.3 pc. IRAS 17527 − . The 1665-MHz OH maser de-tected towards this region at velocity of 11.5 km s − ismore consistent with the NH gas velocity (13.2 km s − )than the H O maser detected at velocity of ∼ -2 km s − bypalla et al. (1991). The 1.1-mm plot (Figure 4) show thatone of the peaks is coincident with the IRAS positionwhile the OH maser is o ff set by ∼ IRAS 18024 − . The OH masers is o ff set by ∼ mu m continuum(Molinari et al. ? ). No cluster was detected by Faustini etal (2009). IRAS 18048 − . The OH masers (detected at the1665-, 1667-MHz, and 1720-MHz) and IRAS source areassociated with di ff erent 1.1-mm peaks and the one closerto the IRAS source is ∼ OH and H O masers(Schutte et al. 1993; Palla et al 1991) peaks at di ff er-ent velocities but at similar velocity ranges. This sourceshows absorption feature at the 1667-MHz OH and aweak maser at the 1720-MHz satellite line which indi-cates that this source may be associated with SNR. IRAS 18089 − + . The OH masertowards this source was firstly detected by Cohen et al.(1988) at the 1665-MHz line. Argon et al. (2000) mappedthis line in arc-second resolution which show three di ff er-ent components. The component which associated withstrongest emission ( ∼ ff set by ∼ ∼
30 Jy). EFC07 also detected an emission at the 1667-MHz line. This means that this isa variable source which is consistent with the daily moni-toring nine-year observations of Goedhart et al. (2009) atthe 6.7 and 12.2 GHz CH OH maser lines. They measurea period of variability as short as less than a month. TheOH masers, 1.1-mm peak, and the IRAS position may bein coincident (Figure 4). These source is associated withH O (palla et al. 1991) and CH OH (Szymczak et al.2000) masers and is also associated with very weak 3.6cm continuum emission, 0.9 mJy (Sridharan et al. 2002).Recent high angular resolution submillimeter observa-tions in various spectral lines by Beuther et al. (2005) de-tect a massive rotating structure perpendicular to an ema-nating outflow which is likely associated with the centralaccretion disk.
IRAS 18090 − . The OH maser emission detectedtowards this source at the two main lines (RHC only) ismuch weaker ( ∼ OH maser (Szymczak et al. 2000). The peakvelocity of the CH OH maser is more consistent with the1667-MHz line than the 1665-MHz. One of the mm peaksis coincident with the IRAS source while the OH maseris o ff set by ∼ IRAS 18102 − . The OH maser detected towardsthis sources at the 1665-MHz (RHC) only. One of the mmpeaks is more consistent with the IRAS source than theOH maser which is o ff set by ∼ OH maser and a 44 mJy radio emis-sion (Sridharan et al. 2002 and reference therein).
IRAS 18144 − . The OH maser detected towardsthis sources at the main lines is a relatively stronger (80Jy) than the other types of masers, CH OH ∼
33 Jy(Szymczak et al. 2000) and H2O, ∼
24 Jy (Palla et al.1991). There is a significant gap, 13 km s − between thecentral velocities of strongest components in the 1665 and1667 MHz lines. The OH maser and the IRAS source arenot closely associated and are not consistent with any ofthe mm peaks to within ∼
18 arcmin. The radio contin-uum emission detected towards this region at 2 and 6 cmis o ff set from the IRAS source by ∼
90 arcsec (Molinariet al. 1998) and no outflow was detected by Zhang et al.(2005).
IRAS 18182 − . The velocity of OH maser de-tected towards this source at the two main lines is con-sistent with the CH OH and H O masers detected bySzymczak et al. (2000) and Beuther et al. (2002a) respec-tively. But although these two later traces were mappedrecently using the VLBI by Sanna et al. (2010) may becoincident with VLA 3.6 cm observations by Zapata elal. (2006), the OH maser mapped by Forster & Caswell(1999) is o ff set by ∼
25 arcsec and the closest mm peak is . A. Edris: OH Masers and the Dust Emissions Towards HMPOs 5
Fig. 2.
The OH (from Foster & Caswell 1999), CH OH andH O masers (from Zapata el al. 2006, cm and the closest mmpeak in the region of IRAS 18182 − o ff set by ∼ IRAS 18566 + . Towards this source one of the1.1 mm peaks is consistent with the IRAS positions. Thishas also been found with 1.2 mm observations by Beutheret al. (2002a). The OH masers have a wide velocity range( ∼
40 km s − ) and the two positions detected by EFC07at the two mainlines are located in the two opposite sidesof the IRAS / mm source (figure 4). This mm peak hasthe strongest flux among all other peaks within 30 ar-cmin. This source is also associated with CH OH maseremission (Sridharan et al. 2002; Szymczak et al. 2000).The H O maser emission was detected by Sridharan etal. (2002), while was not detected by Palla et al. (1991).An outflow was detected by Beuther et al. (2002a) andSridharan et al. (2002) place an upper limit of 1 mJy onthe 3.6 cm radio continuum flux from any source in thisregion.
IRAS 19035 + . This is the sec-ond source with the three tracers, OH, mm, and IRAS arein very good agreement to within 0.05 pc (figure 6). Theposition of the OH maser is taken from the arcsec resolu-tion observations of Argon et al. (2000). It is the strongestOH maser source ( ∼
300 Jy) within this sample. The mmpeak consist with the OH maser has the strongest fluxof the other peaks within 30 arcsec. An outflow and 1.2mm continuum emission were detected by Beuther et al.(2002a).
IRAS 19092 + . The OH maser position measuredby high resolution observations using MERLIN (Edris etal. 2009) is 0.2 pc o ff set from the mm peak. It seems tobe more closer than the IRAS source. A VLA observa-tions of 44-GHz class I methanol masers (Kurtz et al.2004) show a close association between this tracer and Fig. 3.
The o ff sets of the IRAS sources and the closest mmpeak. All IRAS sources are close to the mm peaks to < + the OH masers. This source is also associated with classII CH OH and H O masers.
IRAS 19118 + . The mm and IRAS are seem-ingly closer (to within 12 aresec) than the OH maserwhich is o ff set by ∼ O or CH OH masershave been detected towards this source (Palla et al. 1991;Szymczak et al. 2000).
IRAS 19410 + + . The IRAS, OHand 1.1-mm emission are closely associated within 0.2 pcand consistent with previous 1.2-mm continuum observa-tions as well as CH OH maser(Minier et al. 2005)). Thisobservations show another weaker mm clump with nomid-IR emission. It is associated with weak radio sourceof ∼ ∼ − which falling in theCH OH masers velocity range (14 to 28 km s − ) with sev-eral features peak at 17 km s − (Szymczak et al. 2000).Two outflows was detected by Beuther et al. (2002a) toassociate each of the 1.2 mm clumps.
5. Discussion
It obvious that for those sources with high angular reso-lution observations, their are a very good agreement be-tween the OH masers and the millimeter emission as wellas the IRAS position. Indeed towards IRAS 18089-1732and IRAS 19035 + K. A. Edris: OH Masers and the Dust Emissions Towards HMPOs these sources is IRAS 19092 + ff setfrom the millimeter peak by ∼ The association of infrared emission and maser emissionhas been confirmed by many surveys. Many surveys ofstar forming regions has used the IRAS catalogue viacolor-selected sources (e.g. Palla et. al. 1991). The de-tection rate of up to 26 % of the maser emission has beenfound towards these IR sources. Also The association be-tween the maser emission and mm and sub-mm have beenfound in the case of methanol masers (e.g. Breen et al.2010) and water masers (e.g. Jenness et al. 1995).the asso-ciation OH masers and the mm emission has been foundtowards some sources (e.g. Edris et al. 2005). TowardsThis sample OH maser emission is in more consistentwith the mm peaks than the IR peaks. This means that theOH maser is associated with the colder dust more thanthe hotter one. This consistent with the maser being origi-nated from the outflows or the outer layers of the circum-stellar material. The Elitzur & de Jong (1978) model pro-pose that the OH masers originated from the outer shellof the HII region. however there is no detectable HII re-gions towards these sources. Gray et al. 2003 propose thattowards some sources the OH masers are originated fromdi ff erent layers of the circumstellar disk. The criteria ofchoosing these sample would prefer the later model buthigh angular resolution observations are needed to con-firm this suggestion.
6. Conclusions
The association between OH maser emission and 1.1 mmcontinuum emission towards 27 IRAS sources has beenstudied. The OH maser emission is more consistent withthe mm peaks than the IR peaks. The large positional un-certainty do not allow to give a firm conclusions but to-wards the sources which have been observed at high angu-lar resolutions the three tracers seem to be in correlation.High angular resolution observations are needed to reachto a conclusion about the association between the maseremission and the dust emission.
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Fig. 4.
The position of the OH masers and all mm peaks found within ∼
30 arcmin as well as the IRAS position. The IRAS nameof the source is indicated in the upper left corner of the first three plots. The x-axis represents the right ascension and the y-axisrepresents the declination, both in degrees of arc.
K. A. Edris: OH Masers and the Dust Emissions Towards HMPOs
Fig. 5. same as Figure (4). . A. Edris: OH Masers and the Dust Emissions Towards HMPOs 9
Fig. 6. same as Figure (4).0 K. A. Edris: OH Masers and the Dust Emissions Towards HMPOs