PAH Emission Within Lyman Alpha Blobs
ABSTRACT We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGN). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest frame far infrared) also indicates a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with sub-mm detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with the Lya luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs. Comment: 34 pages, 5 figures, accepted by ApJ
- SourceAvailable from: Simon L. Morris[Show abstract] [Hide abstract]
ABSTRACT: We have used the SAURON panoramic integral field spectrograph to study the structure of the Ly emission-line halo, LAB1, surrounding the submillimetre galaxy SMM J221726+0013. This emission-line halo was discovered during a narrow-band imaging survey of the z= 3.1 large-scale structure in the SSA 22 region. Our observations trace the emission halo out to almost 100 kpc from the submillimetre source and identify two distinct Ly‘mini-haloes’ around the nearby Lyman-break galaxies. The main emission region has a broad line profile, with variations in the line profile seeming chaotic and lacking evidence for a coherent velocity structure. The data also suggest that Ly emission is suppressed around the submillimetre source. Interpretation of the line structure needs care because Ly may be resonantly scattered, leading to complex radiative transfer effects, and we suggest that the suppression in this region arises because of such effects. We compare the structure of the central emission-line halo with local counterparts, and find that the emission-line halo around NGC 1275 in the Perseus cluster may be a good local analogue, although the high-redshift halo is factor of ∼100 more luminous and appears to have higher velocity broadening. Around the Lyman-break galaxy C15, the emission line is narrower, and a clear shear in the emission wavelength is seen. A plausible explanation for the line profile is that the emission gas is expelled from C15 in a bipolar outflow, similar to that seen in M82.Monthly Notices of the Royal Astronomical Society 05/2004; 351(1):63 - 69. · 5.52 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The Large APEX Bolometer Camera, LABOCA, has been commissioned for operation as a new facility instrument t the Atacama Pathfinder Experiment 12m submillimeter telescope. This new 295-bolometer total power camera, operating in the 870 micron atmospheric window, combined with the high efficiency of APEX and the excellent atmospheric transmission at the site, offers unprecedented capability in mapping submillimeter continuum emission for a wide range of astronomical purposes. Comment: Accepted for publication in A&A, 18 pages, 18 figuresAstronomy and Astrophysics 03/2009; 497(3):945-962. · 5.08 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: In May 2007, the Large APEX Bolometer Camera LABOCA was commissioned as a facility instrument on the APEX 12-m submillimetre telescope located at an altitude of 5100 m in northern Chile. The new 870-μm bolometer camera, in combination with the high efficiency of APEX and the excellent atmospheric transmission at the site, offers unprecedented capability in mapping submillimetre continuum emission. An overview of LABOCA and the prospects for science are presented.The Messenger. 09/2007; 129:2-7.
arXiv:1011.3556v1 [astro-ph.CO] 16 Nov 2010
PAH Emission Within Lyman Alpha Blobs
James W. Colbert1, Claudia Scarlata1, Harry Teplitz1, Paul Francis2, Povilas Palunas3,
Gerard M. Williger4, Bruce Woodgate5
We present Spitzer observations of Lyα Blobs (LAB) at z=2.38–3.09. The
mid-infrared ratios (4.5/8µm and 8/24µm) indicate that ∼60% of LAB infrared
counterparts are cool, consistent with their infrared output being dominated by
star formation and not active galactic nuclei (AGN). The rest have a substantial
hot dust component that one would expect from an AGN or an extreme starburst.
Comparing the mid-infrared to submillimeter fluxes (∼850µm or rest frame far
infrared) also indicates a large percentage (∼2/3) of the LAB counterparts have
total bolometric energy output dominated by star formation, although the num-
ber of sources with sub-mm detections or meaningful upper limits remains small
(∼10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright
sources associated with LABs. Four of these sources have measurable polycyclic
aromatic hydrocarbon (PAH) emission features, indicative of significant star for-
mation, while the remaining two show a featureless continuum, indicative of
infrared energy output completely dominated by an AGN. Two of the counter-
parts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH
equivalent widths indicative of large energy contributions from both star forma-
tion and AGN. Most of the LAB infrared counterparts have large stellar masses,
around 1011M⊙. There is a weak trend of mass upper limit with the Lyα lu-
minosity of the host blob, particularly after the most likely AGN contaminants
are removed. The range in likely energy sources for the LABs found in this and
previous studies suggests that there is no single source of power that is producing
all the known LABs.
Subject headings: galaxies: evolution, galaxies: high-redshift, infrared: galaxies
1Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125
2Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT
3Las Campanas Observatory, La Serena, Chile
4Dept. of Physics & Astronomy, University of Louisville, Louisville, KY 40292
6NASA Goddard Space Flight Center, Greenbelt, MD 20771
– 2 –
The Lyα blob (LAB) remains one of the great mysteries of the high redshift universe.
While these extended Lyα nebulae are similar in extent (5-20′′or ∼50-150 kpc) and Lyα flux
(∼1043−44ergs s−1) to high-redshift radio galaxies, blobs are radio quiet and are therefore
unlikely to arise from interaction with jets. They are found almost exclusively within high-
redshift galaxy over-densities (Matsuda et al. 2009; Prescott et al. 2008; Palunas et al. 2004;
Steidel et al. 2000) with none found so far at even moderate redshift (z<0.8; Keel et al.
2009), suggesting strong evolution. After more than a decade of searching, there are still
only a handful of the truly giant (>50 arcsec2, >5×1043ergs s−1) LABs known. However,
deep searches (Matsuda et al. 2004; Saito et al. 2006) show that the blobs are part of a
continuous size distribution of resolved Lyα emitters.
With most lying at the density peak of high redshift structures (Matsuda et al. 2009,
2004; Palunas et al. 2004) and with number densities comparable to galaxy clusters in the
nearby and high-z universe (10−5–10−6Mpc−3; Yang et al. 2009), it seems likely that the
giant LABs are at the very least signposts for regions of massive galaxy assembly, if not
the progenitors of the massive elliptical galaxies themselves. The limited HST imaging of
these objects to date shows some evidence for interaction and merger of multiple compact
objects (Chapman et al. 2004; Francis et al. 2001). Major mergers of high-mass galaxies,
like those predicted to build giant ellipticals, must be occurring at higher redshift (i.e.,
Narayanan et al. 2010; Stewart et al. 2009). The LAB may represent an opportunity for the
study of the merger formation of the most massive galaxies.
One of the biggest unknowns of the blobs is the source of their energy. Matsuda et al.
(2004) found that for at least a third of LABs, including all the biggest and brightest of
them, the galaxies within the blob do not emit enough rest-wavelength UV light to excite
such a vast quantity of hydrogen gas. The exciting ultraviolet illumination could be escaping
along different lines of sight from an obscured AGN (Basu-Zych & Scharf 2004). Many LABs
contain luminous X-ray counterparts (Geach et al. 2009; Yang et al. 2009), while others show
powerful AGN emission lines (Scarlata et al. 2009; Dey et al. 2005; Pascarelle et al. 1996).
Alternatively, outflows could be driving great plumes of gas into the surrounding ambient
medium and producing shocks. While AGNs are known to drive some outflows, supernova-
driven superwinds are also a viable model (Taniguchi & Shioya 2000; Ohyama & Taniguchi
2004). Such outflows would likely take the form of immense bubbles or shells expanding
outwards from the galaxy, some evidence of which has been claimed in the brightest LABs
(Mori & Umemura 2007).
Integral field spectroscopy of the LABs show the large Lyα velocty widths and structure
consistent with superwind outflows (Bower et al. 2004; Wilman et al. 2005; Weijmans et al.
– 3 –
2010), although the systems are complicated enough that other velocity models, like rotation,
can not be completely ruled out. Cooling flows have also been suggested as a possible source
of the extended Lyα emission (Haiman et al. 2000; Francis et al. 2001; Dijkstra et al. 2006).
The primary evidence to support the cooling model are LABs with no apparent internal
power source, even out to the mid-infrared (Nilsson et al. 2006; Smith et al. 2008), and
sources with He II emission with weak to no measurable CIV emission (Prescott et al. 2009;
Scarlata et al. 2009), indicative of the lower temperature gas emission that one would expect
from a cooling flow (Bertone & Schaye 2010).
Mid-infrared and submillimeter imaging show that it is very common that the extended
nebulae of LABs contain sources of extreme infrared luminosity. Powerful Spitzer 24µm
sources have been found within roughly ten LABs, and almost all the most luminous ones,
(Webb et al. 2009; Geach et al. 2007; Colbert et al. 2006; Dey et al. 2005), with fluxes of
0.05-0.86 mJy. Submillimeter flux has been measured for a similar number (Chapman et al.
2004; Smail et al. 2003; Geach et al. 2005; Beelen et al. 2008). Mid-infrared colors suggest
significant quantities of hot dust for these infrared-bright sources (Webb et al. 2009), al-
though whether from AGN or extreme star formation remains unclear.
In this paper we discuss mid-infrared and submillimeter observations of mid-infrared
sources identified within LABs from four different fields, with z=2.38-3.09. We examine both
their Spitzer mid-infrared flux ratios and mid-infrared to sub-mm flux ratios and compare
them to models in order to identify their likely power source, AGN or star formation. We
then look at Spitzer IRS spectra of 6 sources for an even more definitive AGN/star formation
separation. Finally, we look at the possible masses of these infrared sources from within the
LABs. We assume an ΩM=0.3, ΩΛ=0.7 universe with Ho=70 km s−1Mpc−1.
2. Data Acquisition and Reduction
Because of their rarity, most LABs are discovered in small numbers, often one or two
at a time. This has led to a naming system where the LABs in question are often just
referred to as Blob 1 or Blob 2, if they are given any specific name at all. That creates a
problem for a work such as this one, where multiple LABs are being discussed from multiple
fields, all known as Blob 1 or LAB1 or B1 or something similar. Since LABs are large, they
occasionally have multiple counterparts associated with them, which can make it even more
difficult to identify the correct object under discussion.
To address this issue we will use the following naming system in this paper. All LABs
– 4 –
will be referred to as:
LAB[number][letter] J[coordinate of associated field center]
The [number] used is that which has been associated with the LAB in previous publi-
cations, if there has been any. If no previous number has been assigned we will begin the
labeling at LAB1 and count upwards from there. In many cases, the original numbering
included all the detected Lyα emitting sources in the field so just because there is a LAB6
does not indicate there must be a LAB5. While these ”missing” numbers might create some
mild confusion, we found this system to be superior to the certain confusion that would
result from changing the numbers that have already been used to identify these sources from
one paper to the next.
The [letter] refers to the counterpart of the LAB being discussed. Most blob counterparts
have only one associated counterpart and will therefore be given no letter identifier, so the
existence of a letter implies that at some point in the literature, multiple components have
been assigned to the LAB. Discussions of the LABs themselves will never be given a letter.
The [coordinate of the associated field center] is an eight digit code giving the right
ascension and declination (J2000) of the field with which the LAB is associated. Most of
these fields have been observed multiple times with slightly different centers, but for this
paper we have chosen J2217+0017, J1714+5014, J1434+3317, and J2143-4423 to represent
the SSA22, 53w002, NDWFS, and J2143-4423 fields in this study (see below). We found
this method of only providing a field coordinate superior to a full 12-14 digit coordinate
designation as it makes the discussion of object names significantly less cumbersome and
keeps a clear connection with the field and/or structure they have been found within.
Table 1 provides the list of all the LAB infrared counterparts included in this paper,
providing both the new name as well as any previous names by which the LABs have been
2.2. IRAC and MIPS data
The LABs presented in this paper are spread across four different fields: J2143-4423,
SSA22, 53w002, and the NOAO Deep Wide-Field Survey. We assembled all available Spitzer
mid-infrared imaging data, which includes both IRAC and MIPS imaging.
The data for the J2143-4423 field (LAB1 J2143-4423, LAB6 J2143-4423, LAB7 J2143-
4423) come from GO-3699 (PI: Colbert) and were done in a 3 × 5 raster map covering 15′×
25′, centered at α= 21h42m35s, δ = -44◦27′(J2000.0). The total integration times per pixel
– 5 –
were 1800 s for IRAC channels 1-4 and 1818 s for MIPS 24µm. This reached 3 σ depths of
1, 7, and 40 µJy for 4.5, 8, and 24 µm respectively.
For the SSA22 field (see Steidel et al. 2000; Matsuda et al. 2004) we examine the 16
LABs with both an isophotal area greater than 20 square arcseconds and submillimeter data
coverage, excluding only LAB4 J2217+0017 which lies too close to a bright object for an
uncontaminated analysis. We assembled the Spitzer imaging from multiple programs taken
at different epochs, centered roughly at α= 22h17m40s, δ = +00◦17′(J2000.0). The IRAC
and MIPS data come from four programs: GO 30600 (PI: Colbert), GO 3473 (PI: Blain),
and GTO 64 & GTO 30328 (both PI: Fazio). The IRAC data was previously presented
in Webb et al. (2009), but we re-extracted the photometry to ensure uniformity among our
several fields and also extracted to slightly deeper (3σ) depths. The MIPS data presented
here includes new data (GO 30600, see below) not presented in Webb et al. (2009), covering
more sources and greatly increasing the 24 µm depth.
The SSA22 IRAC data from GTO 64 was a deep pair of single pointings covering most of
the known SSA22 blobs, GTO 30328 was a 3 × 4 raster map, while GO 3473 was a smaller 2
× 3 raster map that lies to the east of the majority of the known LAB positions. Altogether
the combined IRAC image maps out a region roughly 20 × 26 arcminutes, ranging in depth
from 1500 to 15,000 seconds. Most of the LABs lie at depths of 4000 s or greater, roughly
corresponding to 3 σ depths of 0.5 and 5 µJy at 4.5 and 8µm respectively. Only one of the
sub-mm detected blobs (LAB10 J2217+0017) completely falls off the area covered by IRAC.
The SSA22 MIPS data from GTO 64 is a single pointing (1120 s), GTO 30328 is a 3
× 3 map built from a set of cluster offsets (1200 s per pixel), and GO 3473 was a set of
pointings targeting known sub-mm galaxies (1200 s). GO 30600 consisted of two parts. The
first was a set of three pointings targeting the sub-mm detected blobs on the outskirts of the
previously taken 24µm data (2700 s each). The second part was an extremely deep pointing
on the central portion of the field (10,800 s) where the biggest LABs (LAB1 J2217+0017
& LAB2 J2217+0017; Steidel et al. 2000) are located. Assembled altogether the MIPS data
covers an area roughly 15 × 26 arcminutes, with the regions covering the LAB locations
ranging from 1200 - 13,000 seconds, with all sub-mm detected LABs observed for at least
3300 seconds, which provides a 3 σ depth of ∼30 µJy.
The 53w002 field, centered at α = 17h14m20s, δ = +50◦15′(J2000.0), contains two LABs
(Keel et al. 1999). The IRAC data come from GTO 211 (PI: Fazio) and were obtained in a
single pointing of 3300 s in all four IRAC bands. The MIPS data are a combination of GO
3329 (PI: Stern), a single 500s pointing, and GO 20253 (PI: Im), a much deeper exposure
of 18720 seconds. The 3 σ depths obtained are 0.6, 5, and 12 µJy for 4.5, 8, and 24 µm
respectively, not accounting for the effect of confusion noise which becomes significant in