A study of the molecular environment of methanol masers and...

What ' s i n the b rew?

A study of the molecular environment of methanol masers

and UCHII regions

Out l i ne o f ta lk

● Low vs high -mass star formation (SF)

● The SF menagerie– UCHII regions, hot and cold cores, methanol masers

● The UNSW Hot Molecular Core survey– The sample

– Observations

– Analysis and results

● Observationally well defined– Long lifetimes (~107 yr) – Many isolated examples– Nearby and often resolved– Collimated jets & dusty disks

● Theoretically well defined– Distinctive SEDs– Clear evolutionary path– Class 0 - Class III

Low vs h igh -mass s ta r fo rmat ion

After Lada et al 1987 & Andre et al 1993

Low vs h igh -mass s ta r fo rmat ion

● Observationally obscure

– Form in clusters within GMCs

– Short evolution time-scale (~105 yr), so evolve onto the main sequence before emerging from cloud

– Highly embedded and so visible in IR or Radio only

Low vs high -mass s ta r fo rmat ion

FarIR

NearIR

Optical


● Observationally obscure

– Form in clusters within GMCs

– Short evolution time-scale (~105 yr), so evolve onto the main sequence before emerging from cloud

– Highly embedded and so visible in IR or Radio only

– Few exampled known - Initial Mass Function is steep● Most lie at distances of kiloparsecs and require

interferometric techniques to resolve them– Gregarious: form exclusively in clustered mode

● Highly energetic processes difficult to disentangle ● In theory, difficult to form

– Low mass formation scenarios does not apply

– Current models: competitive or enhanced accretion


Burning questions:

● Is there a well defined evolutionary sequence similar to low mass stars?

● Do massive protostellar objects evolve disks, jets and outflows similar to LM-SF?

● What can we use as an evolutionary marker in massive protostellar objects?

● Once thought to represent earliest observable stage of massive star formation!

● Found via their very red IR spectra (IRAS)

The SF menager ie – UCH I I reg ions

● Ionised bubbles of gas around early type stars

The SF menager ie – UCH I I reg ions

● SED of a UCHII region

The SF menager ie - ho t co res

● Knots of hot, dense gas● Found near UCHII regions● Embedded within larger

structures -> ‘clumps’● Luminous in infrared

– greater than 104 Lsun● Rich chemistry

MSX 21 m - mid-IR

≤ 18” = 1pc = 200K AU

CH3CN HCN HCO+ CH3OH


Ionised Gas (UCHII region)

Hot Core(NH3)

Clump (C17O)

Cesaroni 2001, 2005

MSX 21 m - mid-IR

≤ 18” = 1pc = 200K AU

● Only a handful of hot cores known.● EG:


≤ 18” = 1pc = 200K AU

Hot Core(NH3)

Cesaroni 2001, 2005

MSX 21 m - mid-IR

≤ 3” ≈ 0.1pc ≈ 20k AU

● Only a handful of hot cores known.● EG:


● T = 100 - 300 K● nH2 > 107 cm-3

● D < 0.1 pc● Outflows● Shocks● HCHII regions?● Multiplicity?

● Internally heated: shells of chemicals.– volatile non-polar ices evaporate first leading to

an ‘onion layer’ effect.

● Chemistry is time-dependent.


33 k AU

1000 AU From Van Dishoeck et al 1998, after Tielens et al 1991

● Abundance depends on physical conditions, initial abundances, geometry ... complex!

● Ideally: Simultaneously coupled radiative transfer and chemical network models.

Hot cores - chemica l mode l s

Rod

gers

& C

harn

ley,

200

1

ABU

ND

ANC

E

TIME (yrs)RADIUS (cm)

The SF menager ie – 'Co ld ' co res

● Analogous to infrared- dark Bok globules

● Also found nearby UCHII regions

● Dense & cool gas

● SED's peak at longer wavelengths (~150µm)

Possible precursors to the hot core stage?

The SF menager ie – CH 3 0H masers

● 6.67 GHz methanol masers only found towards massive star forming complexes

● Radiatively pumped by IR photons and exist in gas with temperatures above 150K

● VLBI observations resolve lines and arcs

CH 3 OH masers as s ignpos ts

Methanol masers towardsIRAS “UCHII” regions

Walsh et al 1998

Parkes & Narrabri


Methanol masers towardsIRAS “UCHII” regions

Parkes & Narrabri

Walsh et al. 1997, 1998.

Sometimes coincident,but often well separated

Isolated

Coincident


● Follow-up observations on 'isolated' masers– 73 maser sites

– SCUBA 450 and 850μm● All directly associated

with clumps of dense gas

● Luminosities >104 Msun

– How do these objects fit into an evolutionary sequence?

Parad igm fo r mass ive SF ?

●What is the link between CH3OH masers and star formation?●Hypothesis: intrinsically linked to Hot Molecular Core stage.

UNSW Hot Mo lecu la r Cores su rvey● 83 methanol maser selected dusty cores

● All associated with thermal continuum emission

– 1.2-mm (SIMBA, SEST), Hill et al 2005

– 450 and 850 µm (SCUBA, JCMT)

– Most associated with mid-IR MSX sources

Isolated Masers

UC HII Region & Masers

450µm (SCUBA)

Different tracers – different ages?

•19 UCHII regions (traced by 8.7 GHz radio)

•59 Isolated maser sites

•5 Dusty cores (seen in thermal emission only)

Walsh et al 1999, 2001, 2003 Hill et al 2005

MSX 8 µm image of the Galactic plane

HMC survey - observa t ions

CH3CN (5-4)

Molecule:

HCN (1-0)

HNC (1-0)

HCO+ (1-0)

N2H+ (1-0)

Rotational Temperatures, Column DensityPositive indicator of hot core chemistry.

In theory, abundance ratio dependant on gas temperature, Critical density probes outer envelope.

Signatures or outfall & inflow,sensitive to optical depth.

Excellent cool dense-gas tracer..

Usage:

CH3OH (2-1) “Temperature” probe.

H13CO+ (1-0)

& (6-5)

13CO (1-0) Beam averaged mass, sanity check


Mopra Specifications (pre 2006):22m Shaped reflector ~34” beam @ 86 GHz85–115 GHz (2.6 3.5 mm) Dual Polarization SIS receiverBandwidth: 64, 128 or 256 MHz Velocity (200 800 km/s)1024 Channels (0.2 0.8 km/s per channel)

Performance:Tsys ~ 150 K – 300 K

Position Switching mode onlyPointing


64 MHz ≈ 180 km/s usable bandwidth


● June -September, 1999 - 2004● 36 observers (see author list Purcell 2006)● Position-switched mode● 600+ spectra● Somewhat 'buggy' data ...

● Technology marches on– These observations could now be completed in a

few weeks with X 125 more bandwidth!

HMC survey - de tec t ions

CH3CN (5-4)

Molecule:

HCN (1-0)

HNC (1-0)

HCO+ (1-0)

N2H+ (1-0)

Detections

CH3OH (2-1)

H13CO+ (1-0)

& (6-5)

13CO (1-0)

Detection rate

58/83 70 %

82/83 99 %

80/83 98 %

82/83 99 %

82/83 99 %

82/83 99 %

79/83 95 %

82/83 99 %

HMC survey - de tec t ions

● First result:

● CH3CN detected towards isolated masers

● The detection of CH3CN towards isolated maser sites strongly suggests that these objects are associated with hot cores and are internally heated.

HMC survey – d i s tances

● Kinematic distances

● Problem:– near-far ambiguity

● Solved for 58 sources by reference to the literature– Formaldehyde

surveys, Hydrogen absorption

HMC survey – luminos i ty

● SED fit with a 2 component greybody curve– Luminosity correct to within a factor of a few

MSX

IRAS

1.2mm SIMBA

850 & 450micronSCUBA

HMC survey - CH 3 CN

CH3CN is brighter and more commonly detected towards UCHII regions than towards isolated maser sources.

18 / 19 UCHII regions40 / 64 Isolated masers

Similar result for H13CO+

Consistent with a fall off in flux with distance in the original radio survey. KS test:

Statistic = 0.48Probability = 0.13%

HMC survey - CH 3 CN

● Could this be accounted for by distance?

Similar distributions No correlation T vs D

HMC survey - rad io de tec t ion l im i t

Limiting distance at which a UCHII region is detectable:

~ 1 mJy # Lyman Photons

FrequencyLuminosity

Kurtz et al 1994

HMC survey - rad io de tec t ion l im i t

Distributions are still significantly different – real difference in detection rate.

Filtered for objects below the radio detection threshold.

HMC survey – der ived parameters

Rotational temperature equilibrium (RTE) analysis for 37 sources.

K=0 K=1 K=2 K=3 K=4

Nu/g

u

Our values for Trot are generally lower compared to previous work utilising data from the higher transitions.

It is likely our survey is sensitive to cooler, more extended gas.

8 > Trot > 130 K, Average = 55 K.

HMC survey – k inemat i cs , HCO +

Most lines exhibit asymmetric line profiles or selfabsorption dips:

BLUE: inflowing motionsRED: outflowing motions.

2 Measurements:

Difference in peak height.or

Difference in peak velocity.

Optically ThickHCO+

Optically ThinH13CO+

HMC survey – k inemat i cs , HCO +

● Adopt the concept of ‘Excess’ E = (Nblue – Nred)/Ntotal

● Find excesses of:

Compared to low-mass class 0 and 1:

0.080.02

Peak BrightnessDelta V

0.210.29

Peak BrightnessDelta V

HMC survey – MSX assoc ia t ions

80 sources have MSX counterparts: 68 seen in emission at 21 µm and 8 µm. 12 seen in absorption as ‘darkclouds’.

7 of the 12 dark clouds exhibit asymmetric HCO+ profiles. 6 of which are skewed to the blue, indicative of inflowing motions.

CH3CN is also common in dark clouds, where it is detected towards 90 %, however this may be due to their near distances.

MSX dark cloud

8 µm

HMC survey – S IMBA assoc ia t ions

● Concurrent project to measure 1.2mm flux

● SIMBA Bolometer– SEST telescope

● Completed in 2004● Allows independent

determination of mass– assuming dust properties

– assuming a temperature

● Now have in dependent M and L measures

Mass - l uminos i ty re la t i on

● M-L relation has lower slope than expected● UCHII regions dominate the upper bins

Mass - l uminos i ty re la t i on

● Sanity check using LTE mass from N2H+

– Similar result. Argues for a UCHII sensitivity limit.

HMC survey – eyeba l l ca rnage

● Line-intensities (brightness temperatures)– ratios unaffected by distance

● Line-luminosities, (correct for distance)● Line-widths (Gaussian FWH) ● Derived abundances and temperatures

– CH3CN, CH3OH ... HCO+, N2H

+, 13CO

● Masses and luminosities● IR and (sub)mm colour ratios & fluxes

● Goal: look for differences between subsets

● Divided the sample into groups:– Radio-loud versus radio-quiet

– CH3CN detected versus no CH3CN detected

– MSX-dark versus MSX bright

– Presence or absence of high velocity line wings

– Presence or absence of blue-skewed HC

● Compared distributions using a KS-test● Looked for differences in the medians

– coupled with a LOW probability that the distributions have the same parent

HMC survey -eyeba l l ca rnage

HMC survey – example

● Compare line ratios for two subsamples

– CH3CN detected vs

– CH3CN not detected

● Most significant:– Ratios with CH3OH


HMC survey – eyeba l l ca rnage


● Find:● UHCII regions have the clearest differences

– Enhanced CH3OH, Trot

● CH3OH also enhanced in sites with CH3CN

● Unexpected: MSX-dark clouds show enhanced line widths– small number statistics

● Sources with or without line-wings or infall profile show no significant differences.

● Single-dish line survey of CH3OH masers

– 70 % associated with hot-core chemistry

– CH3CN at isolated maser sites = internal heating

– CH3CN detected towards 18/19 UCHII regions

– Equal numbers of red & blue HCO+ profiles

– MSX-dark clouds exhibit greater linewidths● May harbour more evolved sources.

– Luminosity-Mass relation L M0.68

● Possible bias in sample

– CH3OH may constitute a crude chemical clock

Summary

Mopra - te lescope i s sues

● UNSW – CSIRO Collaboration– Upgrade of outer surface to 3mm capability– Initial support for non UNSW users– Debug any issues with the hardware and

software– Develop basic reduction software

● Rounding error in control software– Error in frequency up to +/- 1 MHz or +/- 1.5

kms-1

– Fix script developed Chris Philips and Cormac Purcell

● Multiplicative error in correlator software– Data multiplied by fixed factors at random time– Automatically fixed in reduction scripts

Mopra - h i s to r i c ga ins

● Historic changes…

● All years: Focusing● Expect year-to-year gains

Subreflector Adjustment2004

Panel Settings &Subreflector adjustment

2003

Subreflector adjustment2002

Subreflector Adjustment2001

Panel Settings2000

ChangeDate

Mopra - h i s to r i c ga ins

0.58 0.68

0.80 0.94

● Modelled by a 5 element vector of efficiencies

● (2000,2001,2002,2003,2004)● Generated a grid of

model vectors & calculated reduced 2

● 2 weighted Av● (0.58, 0.68, 0.80, 0.94,

1.0)● Distributions of

values >20%

Mopra - beam shape & e f f i c i ency

•2003 Beam●@ 86 GHz

10% Sidelobe

•Compensate by moving subreflector


•2004 Beam-@ 86 GHz

Sidelobe @ ~3%

•More symmetric diffraction pattern


•2003 Beam-gaussian out to 40’’-Side lobe @ ~ 10%-Extends to ~90’’

•2004 Beam-gaussian out to 40’’-Side lobe @ ~ 3%-Extends to ~80’’

•Encircled Power-More in main beam 2004-Increase in beam efficiency


Main Beam 80’’

Extended Beam 160’’


● Use model of Mars and Mercury● Take GTP log and Attenuator settings

– 256 MHz continuum measurement

● Mars 2003: MB = 0.4 & XB = 0.6~37’’ ~35’’ ~34’’

Mopra vs the wor ld

… or at least the SEST

vs

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A study of the molecular environment of methanol masers and...

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