What's in the brew? A study of the molecular environment of methanol masers and UCHII regions

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1 What's in the brew? A study of the molecular environment of methanol masers and UCHII regions

2 Outline of talk 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

3 Low vs high -mass star formation Observationally well defined Many isolated examples Nearby and often resolved Collimated jets & dusty disks Theoretically well defined After Lada et al 1987 & Andre et al 1993 yr) Long lifetimes (~10 7 Distinctive SEDs Clear evolutionary path Class 0 - Class III

4 Low vs high -mass star formation

5 Low vs high -mass star formation 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 Optical Near IR Far IR

6 Low vs high -mass star formation 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 Gregarious: form exclusively in clustered mode Most lie at distances of kiloparsecs and require interferometric techniques to resolve them Highly energetic processes difficult to disentangle In theory, difficult to form Low mass formation scenarios does not apply Current models: competitive or enhanced accretion

7 Low vs high -mass star formation 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?

8 The SF menagerie UCH II regions Ionised bubbles of gas around early type stars Once thought to represent earliest observable stage of massive star formation! Found via their very red IR spectra (IRAS)

9 The SF menagerie UCH II regions SED of a UCHII region

10 The SF menagerie - hot cores MSX 21 m - mid-ir 18 = 1pc = 200K AU CH3CN Knots of hot, dense gas Found near UCHII regions Embedded within larger structures -> clumps Luminous in infrared HCN greater than 104 Lsun Rich chemistry HCO+ CH3OH

11 The SF menagerie - hot cores Only a handful of hot cores known. EG: Cesaroni 2001, 2005 Hot Core (NH3) 18 = 1pc = 200K AU MSX 21 m - mid-ir Ionised Gas (UCHII region) Clump (C17O)

12 The SF menagerie - hot cores Only a handful of hot cores known. EG: Cesaroni 2001, 2005 Hot Core (NH3) 3 0.1pc 20k AU 18 = 1pc = 200K AU MSX 21 m - mid-ir

13 The SF menagerie - hot cores T = K nh2 > 107 cm-3 D < 0.1 pc Outflows Shocks HCHII regions? Multiplicity?

14 The SF menagerie - hot cores T = K nh2 > 107 cm-3 D < 0.1 pc Outflows Shocks HCHII regions? Multiplicity?

15 The SF menagerie - hot cores 1000 AU From Van Dishoeck et al 1998, after Tielens et al k AU Internally heated: shells of chemicals. volatile non-polar ices evaporate first leading to an onion layer effect. Chemistry is time-dependent.

16 ABUNDANCE Rodgers & Charnley, 2001 Hot cores - chemical models RADIUS (cm) TIME (yrs) Abundance depends on physical conditions, initial abundances, geometry... complex! Ideally: Simultaneously coupled radiative transfer and chemical network models.

17 The SF menagerie 'Cold' cores Analogous to infrareddark Bok globules Also found nearby UCHII regions Dense & cool gas SED's peak at longer wavelengths (~150µm) Possible precursors to the hot core stage?

18 The SF menagerie CH30H 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

19 CH3OH masers as signposts Methanol masers towards IRAS UCHII regions Parkes & Narrabri Walsh et al 1998

20 CH3OH masers as signposts Walsh et al. 1997, Methanol masers towards IRAS UCHII regions Isolated Sometimes coincident, but often well separated Parkes & Narrabri Coincident

21 CH3OH masers as signposts 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?

22 Paradigm for massive SF? What is the link between CH3OH masers and star formation? Hypothesis: intrinsically linked to Hot Molecular Core stage.

23 UNSW Hot Molecular Cores survey 450µm (SCUBA) 83 methanol maser selected dusty cores All associated with thermal continuum emission 1.2-mm (SIMBA, SEST), Hill et al and 850 µm (SCUBA, JCMT) Most associated with mid-ir MSX sources MSX 8 µm image of the Galactic plane Isolated Masers Different tracers different ages? 19 UCHII regions (traced by 8.7 GHz radio) 59 Isolated maser sites UC HII Region & Masers 5 Dusty cores (seen in thermal emission only) Walsh et al 1999, 2001, 2003 Hill et al 2005

24 HMC survey - observations Molecule: Usage: CH3CN (5-4) & (6-5) Rotational Temperatures, Column Density Positive indicator of hot core chemistry. HCO+ (1-0) Signatures or outfall & inflow, sensitive to optical depth. H13CO+ (1-0) HCN (1-0) HNC (1-0) In theory, abundance ratio dependant on gas temperature, Critical density probes outer envelope. N2H+ (1-0) Excellent cool dense-gas tracer.. CH3OH (2-1) Temperature probe. CO (1-0) 13 Beam averaged mass, sanity check

25 HMC survey - observations Mopra Specifications (pre 2006): Performance: 22 m Shaped reflector ~34 86 GHz GHz ( mm) Dual Polarization SIS receiver Bandwidth: 64, 128 or 256 MHz Velocity ( km/s) 1024 Channels ( km/s per channel) Tsys ~ 150 K 300 K Position Switching mode only Pointing < 8 arcsec

26 HMC survey - observations 64 MHz 180 km/s usable bandwidth

27 HMC survey - observations June -September, 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!

28 HMC survey - detections Molecule: Detections Detection rate CH3CN (5-4) & (6-5) 58/83 70 % HCO+ (1-0) 82/83 99 % H13CO+ (1-0) 80/83 98 % HCN (1-0) 82/83 99 % HNC (1-0) 82/83 99 % N2H+ (1-0) 82/83 99 % CH3OH (2-1) 79/83 95 % 82/83 99 % CO (1-0) 13

29 HMC survey - detections 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.

30 HMC survey distances Kinematic distances Problem: near-far ambiguity Solved for 58 sources by reference to the literature Formaldehyde surveys, Hydrogen absorption

31 HMC survey luminosity IRAS 1.2mm SIMBA 850 & 450micron SCUBA MSX SED fit with a 2 component greybody curve Luminosity correct to within a factor of a few

32 HMC survey - CH3CN CH3CN is brighter and more commonly detected towards UCHII regions than towards isolated maser sources. 18 / 19 UCHII regions 40 / 64 Isolated masers Similar result for H13CO+ Consistent with a fall off in flux with distance in the original radio survey. KS test: Statistic = 0.48 Probability = 0.13%

33 HMC survey - CH3CN Could this be accounted for by distance? Similar distributions No correlation T vs D

34 HMC survey - radio detection limit Limiting distance at which a UCHII region is detectable: Kurtz et al 1994 ~ 1 mjy # Lyman Photons Luminosity Frequency

35 HMC survey - radio detection limit Limiting distance at which a UCHII region is detectable: Kurtz et al 1994 ~ 1 mjy # Lyman Photons Luminosity Frequency

36 HMC survey - radio detection limit Filtered for objects below the radio detection threshold. Distributions are still significantly different real difference in detection rate.

37 Nu/gu HMC survey derived parameters K=0 K=1 K=2 K=3 K=4 Rotational temperature equilibrium (RTE) analysis for 37 sources. 8 > Trot > 130 K, Average = 55 K. 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.

38 HMC survey kinematics, HCO+ Most lines exhibit asymmetric line profiles or self absorption dips: BLUE: inflowing motions RED: outflowing motions. 2 Measurements: Difference in peak height. or Difference in peak velocity. Optically Thick HCO+ Optically Thin H13CO+

39 HMC survey kinematics, HCO+ Adopt the concept of Excess E = (Nblue Nred)/Ntotal Find excesses of: Delta V Peak Brightness Compared to low-mass class 0 and 1: Delta V Peak Brightness

40 HMC survey MSX associations 80 sources have MSX counterparts: 68 seen in emission at 21 µm and 8 µm. 12 seen in absorption as dark clouds. MSX dark cloud 8 µm 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.

41 HMC survey SIMBA associations 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

42 Mass - luminosity relation M-L relation has lower slope than expected UCHII regions dominate the upper bins

43 Mass - luminosity relation Sanity check using LTE mass from N2H+ Similar result. Argues for a UCHII sensitivity limit.

44 HMC survey eyeball carnage 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+, CO 13 Masses and luminosities IR and (sub)mm colour ratios & fluxes Goal: look for differences between subsets

45 HMC survey -eyeball carnage 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

46 HMC survey example MSX 8 µm image of the Galactic plane Compare line ratios for two subsamples CH3CN detected vs CH3CN not detected Most significant: Ratios with CH3OH

47 HMC survey eyeball carnage Find: UHCII regions have the clearest differences CH OH, plane Trot Enhanced MSX 8 µm image of the 3 Galactic 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.

48 Summary 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 Luminosity-Mass relation L M0.68 May harbour more evolved sources. Possible bias in sample CH3OH may constitute a crude chemical clock

49 Mopra - telescope issues UNSW CSIRO Collaboration Rounding error in control software 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 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

50 Mopra - historic gains Historic changes Date Change 2000 Panel Settings 2001 Subreflector Adjustment 2002 Subreflector adjustment 2003 Panel Settings & Subreflector adjustment 2004 Subreflector Adjustment All years: Focusing Expect year-to-year gains <Relative gains 4 yr plot >

51 Mopra - historic gains Historic changes Date Change 2000 Panel Settings 2001 Subreflector Adjustment 2002 Subreflector adjustment 2003 Panel Settings & Subreflector adjustment 2004 Subreflector Adjustment All years: Focusing Expect year-to-year gains <Relative gains 4 yr plot >

52 Mopra - historic gains Modelled by a 5 element vector of efficiencies (,,,, ) 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%

53 Mopra - beam shape & efficiency GHz 10% Side lobe Compensate by moving subreflector

54 Mopra - beam shape & efficiency 2004 Beam -@ 86 GHz Side ~3% More symmetric diffraction pattern

55 Mopra - beam shape & efficiency 2003 Beam -gaussian out to 40 -Side ~ 10% -Extends to ~ Beam -gaussian out to 40 -Side ~ 3% -Extends to ~80 Encircled Power -More in main beam Increase in beam efficiency

56 Mopra - beam shape & efficiency Extended Beam 160 Main Beam 80

57 Mopra - beam shape & efficiency Use model of Mars and Mercury Take GTP log and Attenuator settings 256 MHz continuum measurement ~37 ~35 Mars 2003: MB = 0.4 & XB = 0.6 ~34

58 Mopra vs the world or at least the SEST vs