Too Large and Overlooked?

(Unexpected) Extended free-free emission towards massive star

formation regions

Steven Longmore (Harvard-Smithsonian Center for Astrophysics)

Michael Burton (UNSW), Eric Keto(CfA), Stan Kurtz (UNAM), Andrew Walsh (JCU)

Talk aims

• Show results from Longmore et al 2009, MNRAS, 399, 861

• What did we learn that may be relevant to planning a future ATCA survey for HCHIIs?

Hunting HCHIIs

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Learn to use your weapon

effectively4. Don't be afraid to ask people

more knowledgeable than you questions

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Hunting HCHIIs

Applying for telescope time

HCHII

UCHII

HCHII

Astronomer

HII Region

ASTRO

Top 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Learn to use your telescope

effectively4. Don't be afraid to ask people

more knowledgeable than you questions

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Learn to use your telescope

effectively4. Don't be afraid to ask people

more knowledgeable than you questions

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Learn to use your telescope

effectively4. Don't be afraid to ask people

more knowledgeable than you questions

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Learn to use your telescope

effectively4. Don't be afraid to ask people

more knowledgeable than you questions

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

A sample of HCHIIs?

• Initial sample of 100 IRAS selected objects– Observe

• Thermal dust• Methanol maser• 8GHz continuum

– Select F8GHz < 3mJy as pre-UCHII sample

• Thesis – Found F24GHz>50mJy towards

50% of pre-UCHII region objects

– From F24GHz/F8GHz postulated this could be sample of HCHIIs

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Don't be afraid to ask people

more knowledgeable than you questions

4. Learn to use your telescope effectively

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Spatial filtering?

• However, array configs very different– 8GHz 6A (6km baselines) – 24GHz H168 (168m

baselines)

• Sensitive to very different spatial scales

• Kurtz et al 1999– Found extended emission

around 12/15 UCHIIs– Up to 5’ (2pc)– Up to an order of magnitude

brighter than “compact” component

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Don't be afraid to ask people

more knowledgeable than you questions

4. Learn to use your telescope effectively

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Observations

• Aim: determine if objects are HCHIIs or extended emission?

• Get reliable SED – 3 different frequencies

• 18GHz• 35GHz• 92GHz

– 3 different array configs – matching beam sizes• H75• H168• H214

ResultsInterpretation of objects

• Confirmed `HCHII’s: - 8GHz = optically-thick free-free - fall below pnt src sensitivity

2. Extended free-free emission - 8GHz = optically-thin free-free - spatially extended - resolved-out at 8GHz

3. Outside primary beam

Implications

• Misinterpret evolutionary stage 1/3 pre-uchii post-uchii

• Potentially underestimate dust masses by factor of two

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Don't be afraid to ask people

more knowledgeable than you questions

4. Learn to use your telescope effectively

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

What to take from this?

• In the hunt for HCHIIs:– Careful using interferometric continuum

observations• High resolution, snap-shot imaging with low

number of antenna particularly susceptible to misinterpretting data

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Don't be afraid to ask people

more knowledgeable than you questions

4. Learn to use your telescope effectively

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Hunting HCHIIsTop 10 hunting tips1. Attend a hunter safety/training

course 2. Learn all you can about what

you are hunting3. Don't be afraid to ask people

more knowledgeable than you questions

4. Learn to use your telescope effectively

5. Expect mistakes, and learn from them

6. Spend as much time as you can out hunting

7. Watch the wind8. Be still9. Be quiet10.Wear a safety harness each

and every time you climb a tree

Thanks