We represent the relation of redshift and luminosity of SFR indicators for the entire emission line galaxies samples (Fig. 15). The loose-, middle- and tight-criterion are shown in panels (a), (b) and (c). The filled and open symbols correspond to the [OII]λ3727Åand
Hα luminosity, respectively. We also include the SDSS-peas galaxies and NTT-peas galaxies samples which are in color blue and light blue. The SDSS-peas samples have both OII and Hα detections. Thus, we show both luminosity of [OII]λ3727Åand Hα which display a comparable order of luminosity in Fig. 15.
Interestingly, our tight-criterion is not effective to select the objects which are high in luminosity of SFR indicators (Fig 15c). It is because our tight-criterion selected samples are high in SSFR .i.e high SFR at a given stellar mass. On the other hand, the SDSS-peas samples are also selected by photometric selection criterion. However, they lead to a different result that show extremely high in luminosity of SFR indicators. This feature could be caused by the SDSS-peas samples are more extreme case compared with our tight-criterion selected samples in the color-color diagram (green star symbols in Figs. 3a, 4a, 5a). However, we do not have many spectroscopic observations in our tight-criterion.
This might lead us to the bias that we do not filter out the most extreme “green pea”- like samples from our tight-criterion in color-color diagrams.
The luminosities of SFR indicators show an upper limit∼1043ergs−1, which is inde-pendent of redshift (dotted line in Fig. 15). This feature was also described by Izotov et al. (2011a) except that they are looking at Hβ luminosity and the upper limit of L(Hβ)
∼ 2.5×1042ergs−1. If we adopt the theoretical ratio for Case B, L(Hβ)=L(Hα)/2.86, the upper limit of L(Hα)∼ 7×1042ergs−1 is consistent with our results. The sample from Izotov et al. (2011a) have lower redshifts (up to z ∼ 0.6). Our results, which contain higher redshift objects, imply that this feature is remarkable not redshift dependent. Izo-tov et al. (2011a) claims that this is probably a negative feedback of mechanism due to the intense UV radiation in these high star-formation samples. However, our entire sam-ples show that this might be just a feature commanly seen in any readshift versus absolute magnitude diagram.
There is a target at z∼1.35, which shows a [OII] luminosity above the limitation, could be very interesting. However, the spectroscopic observation of this target shows that the [OII] emission line is quite broad (∼ 35 ˚A ). The broad emission line imply that this target might have the AGNs containimation which can barely selected out by BPT-diagram in
Figure 15: Redshift versus SFR indicators luminosity diagram of our entire emission line galaxies samples. The loose-, middle- and tight-criterion are shown in panels (a), (b) and (c). The OII and Hα luminosity correspond to the filled and open symbols, respectively.
We also include the SDSS-peas galaxies and NTT-peas galaxies samples which are in color blue and light blue. The SDSS-peas samples have both OII and Hα detections. Thus, we show both luminosity of OII and Hα which display a comparable order of luminosity.
The luminosity of SFR indicators show a upper limit∼1043ergs−1that independent with redshift (dotted line).
this such of high redshift.
Chapter 7 Summary
We developed a method based on broad-band photometry to isolate objects similar to
“green pea” galaxies (Cardamone et al., 2009) and Luminous Compact Galaxies (LCGs) (Itozov et al. 2010a) in some various redshift ranges up to z∼1.5. We extend our method to several deep photometric archive datasets which are UKIRT infrared deep sky survey - Ultra Deep Survey (UKIDSS-UDS), Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) and COSMOS-UltraVISTA survey. For convenience, all the magnitudes in optical and NIR filter sets in each catalog are converted to those of the SDSS(u, g, r, i, z) and UltraVISTA(J, H, Ks) filters.
To define our selection criteria, we use 80 low-redshift SDSS peas spectra (z∼0.3, Cardamone et al., 2009) and 8 higher-redshift ESO-NTT peas spectra (z∼0.6, Bamford et al., 2014) as spectrum templates. Convolving these spectrum templates with broad-band photometric system enables us to define the peas selection criteria in color-color diagrams.
Thanks to the deep photometric datasets available (UDS-DR10, CFHTLS+Palomar and COSMOS+UltraVISTA), we can extend our broad-band method to select the r-, i-, z-, J-peas which represent the “green pea” galaxies at z∼0.25, z∼0.55, z∼0.85, z∼1.5 for all the photometric catalogs.
We also combine the spectroscopic data for each of our catalogs. Then, we select a very loose photometric criterion by redshift distribution of the spectroscopic data. We further divide our spectroscopic data into two more smaller parts: middle- and tight-criterion which are more consistent with the distribution of “green pea” galaxies in color-color
diagrams.
From the emission line information of our spectroscopic sample, we obtain the fol-lowing results:
1. The global properties of our tight-criterion selected objects are low in stellar mass (M∗∼109M⊙) and low metallicity (12+log(O/H)∼8.0) compared with normal galaxies.
However, they display high in star formation rate compared with their given stellar mass (SSFR∼10−9yr−1).
2. The results of K-S test for SSFR represent that our tight-criterion selected objects are significantly different from loose-criterion selected objects. This indicates that our tight-criterion is efficient to select the high SFR objects in their given stellar mass.
3. Because the temperature sensitive line [OIII]λ4363Åis too weak to be observed, we ultilize the emprical methods (N2-method and R23-method) to derive the metallicity for our samples. The results of mass-metallicity relation (MZR) and luminosity-metallicity relation (LZR) show that our samples are consistent with others’ work. However, the MZR and LZR results show that our tight-criterion selected objects are not significantly different with middle- and loose-criterion selected objects. This analysis is, however, limited by the double-value solutions for the metallicity derived by the R23-method.
4. If we only look at the metallicity which is derived by R23-method, our tight-criterion selected objects are almost around 12+log(O/H)T e∼ 8.0. This could imply that our tight-criterion selected objects are more likely single-value at 12+log(O/H)T e∼ 8.0. The MZR for our tight-criterion selected samples might be similar to the high redshift objects. Beside that, the LZR for our tight-criterion selected samples could be more consistent with the luminous compact galaxies (LCGs) samples which share similar properties with metal-poor star-forming galaxies at z≤ 1.0 (Itozov et al. 2011a).
5. The luminosities of SFR indicators show an upper limit ∼1043ergs−1, which is independent of redshift (dotted line in Fig. 15). This feature was also described by Izotov et al. (2011a) except that they are looking at Hβ luminosity and the upper limit of L(Hβ)
∼ 2.5×1042ergs−1. If we adopt the theoretical ratio for Case B, L(Hβ)=L(Hα)/2.86, the upper limit of L(Hα)∼ 7×1042ergs−1 is consistent with our results. The sample from
Izotov et al. (2011a) have lower redshifts (up to z ∼ 0.6). Our results, which contain higher redshift objects, imply that this feature is remarkable not redshift dependent. Izotov et al. (2011a) claims that this is probably a negative feedback of mechanism due to the intense UV radiation in these high star-formation samples. However, our entire samples show that this might be just a feature commanly seen in any readshift versus absolute magnitude diagram.
Appendix A
Conversions between Photometric Systems
For the convinence, all the optical filters in each of the catalogs are transfered into the SDSS base filters. We adopt the following equations to do the conversion between UDS and COSMOS with the SDSS filters.
gSDSS = V + 0.72 (B - V) - 0.13 (similar with the equation from Jester et al. 2005) rSDSS = r’ + 0.035 (r’ - i’ -0.53) - 0.15 (SDSS website)
iSDSS = i’ + 0.041 (r’ - i’ - 0.21) (SDSS website) zSDSS = z’ - 0.03 (i’ - z’ - 0.09) (SDSS website)
The transformation for the UDS Rc filter to r’ is given by:
r’ = V - 0.84 (V - RcU DS) + 0.13 (Fukugita et al. 1996)
In the case of CFHTLS, the terms between MegaCam and SDSS filter can be described by following equations:
gSDSS = gM ega+ 0.195 (gM ega- rM ega) rSDSS = rM ega+ 0.011 (gM ega- rM ega) iSDSS = iM ega+ 0.079 (rM ega- iM ega) zSDSS = zM ega- 0.099 (iM ega- zM ega)
Those equation are quote from the CFHTLS website and all the transformations are in AB magnitude.
On the other hand, all the NIR filters data are transfered into UltraVISTA filter base observation. Because of the Palomar filter instruments are resembling the UltraVISTA filter base, we only achieve the filter transformation from UDS WFCAM to UltraVISTA VIRCAM.
J2M ASS = JU DS - 0.01 - 0.03 (JU DS - HU DS) + 0.1 H2M ASS = HU DS + 0.01 + 0.065 (HU DS - KU DS) Ks2M ASS = KU DS - 0.072 (HU DS - KU DS)
Remind here that those equations (Hewett et al., 2006) are base on Vega magnitude.
The offsets within Vega and AB magnitude are display as:
JAB = JV ega + 0.938 HAB = HV ega + 1.379 KsAB = KsV ega + 1.9
Although the 2MASS filter sets are tied to UltraVISTA photometry systems, they still need to do slightly calibration between them by (From the VISTA website):
JU V IST A=J2M ASS-0.077 (J2M ASS - H2M ASS) + 0.1 HU V IST A=H2M ASS+0.032 (J2M ASS - H2M ASS) + 0.1 KsU V IST A=Ks2M ASS+0.01(J2M ASS - Ks2M ASS)
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