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The infrared environments of masers associated with star formation

James M. De Buizer Gemini Observatory


Conclusions Brazil Maser Meeting 2001 Conclusion #1:
The IR regime complements radio continuum observations and offers new insights into maser environments


The combination of mid-IR, near-IR, and radio continuum observations will reveal the majority of the stellar sources in the vicinity of the masers
G35.20-1.74

Masers

· To better understand the maser phenomena we must know the locations of ALL the associated young stellar sources · Massive stars form in clusters with variety of masses and states of evolution

UC HII
Contours: 2cm (Wood & Churchwell 1989)


What Does the IR Trace?
Near Infrared (1-2 um)
­ Photons are usually photospheric or reflected and/or scattered photosperic photons ­ The 2.122 um emission line of H2 can be used to map outflows

Thermal Infrared (3-30 um)

­ Heat radiation from circumstellar dust ­ From 1000 K at 3 um to 100 K at 30 um


Conclusions Brazil Maser Meeting 2001 Conclusion #2:
Masers appear to be more closely associated with IR sources than cm radio continuum


Masers appear to be more closely associated with IR sources the cm radio continuum

Median separation water maser to radio UCHII regions: ~18800 AU (Hofner & Churchwell 1996) Median separation water maser to MIR sources: ~8700 AU (De Buizer et al. 2005)


All masers appear to be closely associated with regions of hot-warm (300-30K) thermal dust emission
cm continuum detection rate towards methanol/ water masers: ~20%
(Walsh et al. 1998; Beuther et al. 2002)

MIR detection rate towards methanol masers: ~70%
(De Buizer et al. 2000; Walsh et al. 2001)

MIR detection rate towards water masers: ~80%
(De Buizer et al. 2005)

Sub-mm/mm detection rate towards methanol/ water masers: ~100%
(Walsh et al. 2003; Beuther et al. 2002)


Conclusions Brazil Maser Meeting 2001 Conclusion #3:
Hot cores associated with masers can be viewed in the mid-infrared and may help constrain young massive stellar accretion models


Greyscale ­ 2cm radio continuum (Cesaroni et al. 1998) Pink contours ­ NH3 hot core (Cesaroni et al. 1998) Blue Contours ­ Mid-IR 10 um continuum (De Buizer et al. 2002)


Water and methanol masers offset from UC HII regions trace mid-IR sources that are in some cases HMPOs (or HMCs)
G29.96-0.02 18.3 µm

L =18000 L

*

sun

De Buizer, Osorio, & Calvet (2005)


Water and methanol masers offset from UC HII regions trace mid-IR sources that are in some cases HMPOs (or HMCs)
G45.07+0.13 12.3 µm

L =25000 L

*

sun

De Buizer et al. 2003; De Buizer, Osorio, & Calvet (2005)


Conclusions Brazil Maser Meeting 2001 Conclusion #4:
The mid-infrared is ideal for testing the hypothesis that masers are located in accretion disks, and near-IR H2 emission may trace outflows from these disks


Methanol masers are linearly distributed 50% of the time and so might generally trace disks
G305.21-0.20

·Only a small number of linearly distributed methanol masers actually have velocity gradients (Walsh et al. 1998) ·De Buizer et al. (2005) show that water and OH masers are also linearly distributed ~50% of the time!


Massive stars and (especially) their disks are hard to observe
· Generally FAR away (few kpc, rather than few pc) · Massive stars form in clusters · Form in the densest and deepest parts of giant molecular clouds · Confusion between disk and nearby sources, outflow, and envelope, UC HII emission


Outflows perpendicular to the disk plane would confirm the maser/disk hypothesis
Disk accretion....

Since direct detection of the thermal emission from the disks is difficult, we need indirect evidence that masers reside in disks Outflows!

Is accompanied by outflow


Surprisingly, near-IR outflow observations in H2 showed emission PARALLEL to maser distributions, not perpendicular
De Buizer (2003) surveyed sites of linearly distributed methanol masers at CTIO
­ ONLY 2 had emission perpendicular to the maser distribution ­ 12 (86%) had emission parallel to the maser distribution
De Buizer (2003) G319.95-0.20 G320.23-0.28


Surprisingly, near-IR outflow observations in H2 showed emission PARALLEL to maser distributions, not perpendicular
De Buizer (2003) surveyed sites of linearly distributed methanol masers at CTIO
­ ONLY 2 had emission perpendicular to the maser distribution ­ 12 (86%) had emission parallel to the maser distribution
De Buizer (2003) G320.23-0.28


Methanol masers may instead trace outflow from massive young stars

· Perhaps the masers are excited in the outflowing material, on the internal working surfaces, or on the cavity walls · However, near-IR H2 can be radiatively excited by massive stars UV flux, and not only in outflows · We need another independent outflow tracer to be sure


ATCA SiO maps confirm that outflows are dominantly at the same position angle as the linear methanol maser distributions
G318.95-0.20

· 5 sites where SiO (6-5) was detected with JCMT, were followed up by mapping in the SiO (2-1) line at ATCA
Grayscale=NIR H
2

De Buizer, Redman, Feldman, Longmore, & Caswell (in prep)


ATCA SiO maps confirm that outflows are dominantly at the same position angle as the linear methanol maser distributions
G320.23-0.28

· 5 sites where SiO (6-5) was detected with JCMT, were followed up by mapping in the SiO (2-1) line at ATCA
Grayscale=NIR H
2

De Buizer, Redman, Feldman, Longmore, & Caswell (in prep)


High-res images are showing circumstellar MIR emission commonly comes from outflows not disks
G35.20-0.74

De Buizer (2006)

De Buizer 2006

· Dust continuum from outflow dominates the MIR emission from this source · Masers, including the OH, appear to be in the outflow cavity walls


Linearly distributed masers and/or extended MIR may generally come from outflows, not disks

Gemini/T-ReCS 18um
De Buizer, Redman, Feldman, Longmore, & Caswell (in prep)

· MIR images appear elongated and disk-like · Masers in a disk? No...


Linearly distributed masers and/or extended MIR may generally come from outflows, not disks

MIR dust emission

SiO Outflow

De Buizer, Redman, Feldman, Longmore, & Caswell (in prep)

· MIR elongation and maser angle same as SiO outflow angle!


· The IR regime still complements radio continuum observations and offers new insights into maser environments, esp. at high angular resolution · All masers still appear to be closely associated with regions of hot-warm (300-30 K) thermal dust emission traced by MIR and sub-mm emission · Water and methanol masers offset from UC HII regions trace mid-IR sources that are in some cases HMPOs · NIR H2 and mm SiO maps confirm that outflows are dominantly at the same position angle as the linear methanol maser distributions · High-res images are showing circumstellar MIR emission commonly comes from outflows, not disks

Newer Conclusions Conclusions

Brazil Maser Meeting 2001